In my Cat25' I have two batteries in series. One was no longer holding a charge so I pulled it and replaced it a couple of weeks ago. Was at the marina installing it this afternoon and noticed I had picked up a "Marine Starting" battery, the other (good) battery is a "Marine Deep Cycle" battery. So... am I headed for the return line (if I can find my receipt...) or are these the same thing? If not, can I still safely connect, in series, these two batteries? Thanks, Kevin
Battery Question
- Thread starter KevinF chicago
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Are You Sure of Series Connection?
Kevin: If the batteries are wired in series the total voltage is the sum of the voltage ratings of each of the batteries. I would think that they should be wired in parallel (positives connected together and negatives connected together) and both be of the same rating (i.e., 12 volt if that is your system).
Kevin: If the batteries are wired in series the total voltage is the sum of the voltage ratings of each of the batteries. I would think that they should be wired in parallel (positives connected together and negatives connected together) and both be of the same rating (i.e., 12 volt if that is your system).
Do you have a 1-2-both battery switch?
Kevin, Do you have a 1-2-BOTH battery switch. Idealy, your battery system should consist of one starting and one deep cycle battery. The batteries are wired to the switch to isolate them. One switch position (1 or 2) is used to start the boat. The other switch position should be your house bank (the deep cycle battery). If your starting battery runs low or dead you can use the "BOTH" position to parallel the two batteries for additional starting power. On my boat, I have two starting batteries and no deep cycle (the boat came that way and I'm just waiting for one battery to die before I buy a deep cycle). I use battery 2 to start the boat because the alternator is wired to that battery. If I want to use the alternator to charge the house bank I just put the battery switch to "BOTH".
Kevin, Do you have a 1-2-BOTH battery switch. Idealy, your battery system should consist of one starting and one deep cycle battery. The batteries are wired to the switch to isolate them. One switch position (1 or 2) is used to start the boat. The other switch position should be your house bank (the deep cycle battery). If your starting battery runs low or dead you can use the "BOTH" position to parallel the two batteries for additional starting power. On my boat, I have two starting batteries and no deep cycle (the boat came that way and I'm just waiting for one battery to die before I buy a deep cycle). I use battery 2 to start the boat because the alternator is wired to that battery. If I want to use the alternator to charge the house bank I just put the battery switch to "BOTH".
MIsmatch can be a Problem
Mismatched batteries can be a problem whether wired in series or in parallel. They will probably perform at less than optimum performance. As the previous thread indicated, they must be wired in either series or in parallel depending on the voltage requirements of the system and the battery voltage. If the system is 12V and the batteries are 12V they must be wired in parallel. If the system is 12V and the batteies are 6V they must be wired in series. If the batteries are wired through a 1-2 switch, none of this applies, unless operating on both. If they are wired in parallel, one of the batteries will tend to carry most of the load and will get most of the charge. If wired in series both batteries will get the same charge and will discharge at the same rate. The problem is that there is a difference in efficiency or heat generattion. It will work, but is not optimum.
Mismatched batteries can be a problem whether wired in series or in parallel. They will probably perform at less than optimum performance. As the previous thread indicated, they must be wired in either series or in parallel depending on the voltage requirements of the system and the battery voltage. If the system is 12V and the batteries are 12V they must be wired in parallel. If the system is 12V and the batteies are 6V they must be wired in series. If the batteries are wired through a 1-2 switch, none of this applies, unless operating on both. If they are wired in parallel, one of the batteries will tend to carry most of the load and will get most of the charge. If wired in series both batteries will get the same charge and will discharge at the same rate. The problem is that there is a difference in efficiency or heat generattion. It will work, but is not optimum.
Thank you
Thanks all for the battery education... Yes, I have a 1-2-Both switch. To be honest, have no idea if I'm wired in series or in parallel (will look this weekend). Thanks again for your help! Kevin "Hermes"
Thanks all for the battery education... Yes, I have a 1-2-Both switch. To be honest, have no idea if I'm wired in series or in parallel (will look this weekend). Thanks again for your help! Kevin "Hermes"
don't do it if
your older battery is more than 6 months old.I am assuming 2 12 volt batteries in parallel. Also, the two batteries need to be identical. Same make, model, and capacity. If they aren't the weaker battery will be constantly draining the stronger battery when not being charged and they will both fail in short order. Then you will be replacing both again. Either run your older battery single until it dies, or replace both now as a matched pair(recommended).
your older battery is more than 6 months old.I am assuming 2 12 volt batteries in parallel. Also, the two batteries need to be identical. Same make, model, and capacity. If they aren't the weaker battery will be constantly draining the stronger battery when not being charged and they will both fail in short order. Then you will be replacing both again. Either run your older battery single until it dies, or replace both now as a matched pair(recommended).
Not an Easy Answer
This could lead to a very interesting discussion, but which may have little to do with batteries. The easy answer is always to go spend money and remove the doubt. In life, this tends to be a very expensive. The expression "Any job worth doing is worth doing right" is one expression which should be banned from intelligent conversation. One young man who worked for me had the philosophy of "Any job worth doing is worth over doing". He was a very expensive young man to have working for me. I disagree with Ruedi who said, “Don’t do it”. I have about seventeen years experience with batteries, both design and application. Admittedly very little of it was with lead acid batteries. A decision of whether or not to do it is a very complicated individual decision. The easy decision is to just go out and spend more money and buy two new batteries. That may not be necessary and is probably wasteful. Batteries can be very tolerant of operating conditions. Lead acid batteries tend to operate in the same voltage range. There are variations, but generally two batteries in parallel can tolerate the differences. For periods during the discharge cycle one battery will become dominant and it will discharge at a higher rate until the other battery catches up and then the other battery becomes dominant. I have seen batteries in parallel, which were terribly mismatched, which performed satisfactorily for years. What has to be done is to look at the cost of setting up a better system. In this case it would be the cost of buying two new batteries. That must be weighed against the likelihood and consequences of failure, if left as is. The consequences of failure are the cost of two new batteries plus whatever consequences might result. The other consequence is the possibility of damage to other equipment or the inconvenience or danger if there is a battery failure. The other thing, which can be considered, is the rate of failure. Is it apt to be a catastrophic failure or will it be a gradual failure? In this case I would expect a gradual deterioration of one battery, but the other battery will continue to operate if the bad battery is removed from the circuit. Keep in mind that no matter what you do they will ultimately fail anyway, unless you replace the batteries on an annual basis and they still may fail. If it was I and a failure is not apt to strand me somewhere for an unacceptable period of time, I would go ahead and operate the batteries in parallel or in series as the case may be. I would also apply this same logic to the person who said to replace all of the lines rather than clean them. I would clean them. A failure of a sheet or other control line is generally not catastrophic.
This could lead to a very interesting discussion, but which may have little to do with batteries. The easy answer is always to go spend money and remove the doubt. In life, this tends to be a very expensive. The expression "Any job worth doing is worth doing right" is one expression which should be banned from intelligent conversation. One young man who worked for me had the philosophy of "Any job worth doing is worth over doing". He was a very expensive young man to have working for me. I disagree with Ruedi who said, “Don’t do it”. I have about seventeen years experience with batteries, both design and application. Admittedly very little of it was with lead acid batteries. A decision of whether or not to do it is a very complicated individual decision. The easy decision is to just go out and spend more money and buy two new batteries. That may not be necessary and is probably wasteful. Batteries can be very tolerant of operating conditions. Lead acid batteries tend to operate in the same voltage range. There are variations, but generally two batteries in parallel can tolerate the differences. For periods during the discharge cycle one battery will become dominant and it will discharge at a higher rate until the other battery catches up and then the other battery becomes dominant. I have seen batteries in parallel, which were terribly mismatched, which performed satisfactorily for years. What has to be done is to look at the cost of setting up a better system. In this case it would be the cost of buying two new batteries. That must be weighed against the likelihood and consequences of failure, if left as is. The consequences of failure are the cost of two new batteries plus whatever consequences might result. The other consequence is the possibility of damage to other equipment or the inconvenience or danger if there is a battery failure. The other thing, which can be considered, is the rate of failure. Is it apt to be a catastrophic failure or will it be a gradual failure? In this case I would expect a gradual deterioration of one battery, but the other battery will continue to operate if the bad battery is removed from the circuit. Keep in mind that no matter what you do they will ultimately fail anyway, unless you replace the batteries on an annual basis and they still may fail. If it was I and a failure is not apt to strand me somewhere for an unacceptable period of time, I would go ahead and operate the batteries in parallel or in series as the case may be. I would also apply this same logic to the person who said to replace all of the lines rather than clean them. I would clean them. A failure of a sheet or other control line is generally not catastrophic.
Kevin Some good advice here, but no one answered your original question. Marine starting batteries ARE DIFFERENT than deep cycle batteries. From West Marine's Advisor: Deep Cycle Batteries -------------------------------------------------------------------------------- What they do Deep cycle marine batteries are designed to run the electrical loads on a boat when no charge source is available (e.g. shorepower charger, engine alternator, solar panel). Compared to starting batteries, their design features thicker plates with a high content of antimony. Deep cycle batteries are a kind of savings account into which energy is deposited or withdrawn from. In difference to starting batteries, which deliver high bursts of energy for short periods, deep cycle batteries recover fully after being heavily discharged over longer periods. Your boat your choice depending on what you need the batteries for. With your C25 I'm guessing you have an outboard engine. So, you need the two batteries for a house bank. Unless you have an electric start engine, you don't need a starting battery. If it were me, I'd simply use the two batteries, but when using them I'd put the switch on both because a larger house bank lasts longer. That opens a whole new discussion... Stu see the link to West Marine Advisors.
Dan
Is your expertise in backup or communication systems, ie nicad? These behave very differently than lead acid. My experience is in large lead acid storage batteries for off-grid home solar/hydro stand alone electrical systems. Much larger and longer lived than smaller marine applications. Wht I've seen in lead acid batteries is that when parallel strings that are mismatched sit in an idle state(neither charging or discharging significantly) the stronger battery bank will push current into the weaker, creating heat in the weaker and discharging the stronger. Granted, the scale is different, but the concept is the same. Mismatched parallel strings in lead acid batteries will shorten the life and performance significantly. Its not a big deal when you are talking about two 90 amp hour batteries that cost less than $100 each and last 3-4 years, but it is there, none the less. Thats my 2 cents. I had a guy work for me that said " there is never enough money to do it right the first time, but there is always enough money to do it over again"
Is your expertise in backup or communication systems, ie nicad? These behave very differently than lead acid. My experience is in large lead acid storage batteries for off-grid home solar/hydro stand alone electrical systems. Much larger and longer lived than smaller marine applications. Wht I've seen in lead acid batteries is that when parallel strings that are mismatched sit in an idle state(neither charging or discharging significantly) the stronger battery bank will push current into the weaker, creating heat in the weaker and discharging the stronger. Granted, the scale is different, but the concept is the same. Mismatched parallel strings in lead acid batteries will shorten the life and performance significantly. Its not a big deal when you are talking about two 90 amp hour batteries that cost less than $100 each and last 3-4 years, but it is there, none the less. Thats my 2 cents. I had a guy work for me that said " there is never enough money to do it right the first time, but there is always enough money to do it over again"
Experience
My experience is in some fairly exotic batteies, but does include NiCd. I have also had some experience in paralleling mismatched lead acid batteries on my 5th Wheel. Unless one of the batteries has gone completely south they will operate in parallel. One battery will tend to carry more current during parts of the discharge cycle. I can't say for for sure how much the life of one battery might be shortened except for individual incidents. I did add a second battery to my fifth wheel in parallel. The new battery failed after three years. The old battery is still going after about eight years. Since I have had battery failures after three years on single well treated batteries, I cannot say whether the failure of the good battery was due to the operating conditions or whether it would have failed anyway. My comments stand. My point was not the operation of lead acid batteries. My point is that it is not an easy solution. Automatically saying that new batteries should be bought is not neccessarily the right answer. Some thought should be put into the process. The same logic should be used in any decision in life in which the decision is whether to repair, clean, etc or to go out and buy a new replacement.
My experience is in some fairly exotic batteies, but does include NiCd. I have also had some experience in paralleling mismatched lead acid batteries on my 5th Wheel. Unless one of the batteries has gone completely south they will operate in parallel. One battery will tend to carry more current during parts of the discharge cycle. I can't say for for sure how much the life of one battery might be shortened except for individual incidents. I did add a second battery to my fifth wheel in parallel. The new battery failed after three years. The old battery is still going after about eight years. Since I have had battery failures after three years on single well treated batteries, I cannot say whether the failure of the good battery was due to the operating conditions or whether it would have failed anyway. My comments stand. My point was not the operation of lead acid batteries. My point is that it is not an easy solution. Automatically saying that new batteries should be bought is not neccessarily the right answer. Some thought should be put into the process. The same logic should be used in any decision in life in which the decision is whether to repair, clean, etc or to go out and buy a new replacement.
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