When I purchased my boat last fall it came with 2 deep cycle batteries. When I replace one of the batteries I would assume It would make more sense to get a starting battery. I wouldn't think a deep cycle battery would be the best choice for engine starting. Would it make more sense to have one of each?
Replacing Battery
- Thread starter ChuckH
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Chuck:
I believe that everyone is going to agree that deep cycle batteries are the way to go for starting & housekeeping. If you check out some previous posts, I have never seen any other recommendation.
I believe that everyone is going to agree that deep cycle batteries are the way to go for starting & housekeeping. If you check out some previous posts, I have never seen any other recommendation.
The ex-wife's hair dryer sucked up 1000 watts for 5 minutes. That is around 83 amps at 12 volts. A starter motor will draw 1400 watts (A very large starter motor BTW) or 116 amps for at most 10 seconds.
83*5/60=6.9 AH to run the hair dryer
116*10/3600=0.32 AH to start the motor
Deep cycles can start motors fine. The only problem you have to address is the redundant battery capability so you can have a charged battery to start the motor. This can be accomplished in a variety of ways.
Some things to consider
1) The larger the bank you draw your house loads from the smaller the actual discharge from each battery. This helps prolong battery life as each bat sees a smaller discharge depth
2) Automatic charging solenoids/diodes/doohickeys prevent you from administratively disconnecting one battery from the bank to reserve it for the next morning's engine start, which is why I prefer a manual 3-way switch.
3) The way you use the boat (day sail only/cruising/...) has a decided effect on how the batteries are used. If all you do is say sail, never anchor out and don't sail at night then you might not even need a deep cycle battery at all. I know on my Catalina 30 all we did was run the anchor light and a few cabin lights at night and we had 2 start batteries for our only bank. Worked fine but they also saw almost no drain.
So you have to know the loads, the time the load will be on the bank, how much recharging you can do and when that will occure and then balance that with the occasional use of the boat in other than normal fashion. A daysailor may be able to get away with a very small battery but if he sants to anchor out occasionally then he would want to consider that in the purchase as it may drive the decision to get a bigger battery.
For planning factors use a starter battery if you are never going to draw it down below 95% charged between charges. Anything more than that will make deep cycle more cost effective.
83*5/60=6.9 AH to run the hair dryer
116*10/3600=0.32 AH to start the motor
Deep cycles can start motors fine. The only problem you have to address is the redundant battery capability so you can have a charged battery to start the motor. This can be accomplished in a variety of ways.
Some things to consider
1) The larger the bank you draw your house loads from the smaller the actual discharge from each battery. This helps prolong battery life as each bat sees a smaller discharge depth
2) Automatic charging solenoids/diodes/doohickeys prevent you from administratively disconnecting one battery from the bank to reserve it for the next morning's engine start, which is why I prefer a manual 3-way switch.
3) The way you use the boat (day sail only/cruising/...) has a decided effect on how the batteries are used. If all you do is say sail, never anchor out and don't sail at night then you might not even need a deep cycle battery at all. I know on my Catalina 30 all we did was run the anchor light and a few cabin lights at night and we had 2 start batteries for our only bank. Worked fine but they also saw almost no drain.
So you have to know the loads, the time the load will be on the bank, how much recharging you can do and when that will occure and then balance that with the occasional use of the boat in other than normal fashion. A daysailor may be able to get away with a very small battery but if he sants to anchor out occasionally then he would want to consider that in the purchase as it may drive the decision to get a bigger battery.
For planning factors use a starter battery if you are never going to draw it down below 95% charged between charges. Anything more than that will make deep cycle more cost effective.
Chuck-- a wise decision. Also, rid yourself of the annoyance of that 1-both-2-off switch. At NO time should you ever charge or discharge the batteries separately-- unless you want to shorten their lives (battery murderer!). As one bank they should be always tied together, charged and discharged together, and stored, maintained and replaced together.
On Diana (H25) I have two size-24 house deep-cycle batteries which are one bank. They are wired to one Blue Sea off-on switch and are never separated. The 3rd battery is a size-24 starting battery for the (outboard) engine. This CAN be used for the house circuits in an emergency (which would be a complete failure of BOTH house batteries at once; so how common is that?). The motor's alternator (tiny as it is) CAN charge the house bank if necessary. Also the 115-vac charger CAN be used to charge the engine battery (as a second bank)-- but otherwise in all normal cases the engine (starting) bank is entirely separate from the house (deep-cycle) bank.
(If the engine starting battery fails I have to pull-start the motor. That's good enough as a fail-safe as it's not that difficult and a cheap solution.)
So it comes to this-- never should two different kinds of battery be combined in one bank; never should multiple batteries of the same bank be separated. Unless you have money (and boat) to burn.
On Diana (H25) I have two size-24 house deep-cycle batteries which are one bank. They are wired to one Blue Sea off-on switch and are never separated. The 3rd battery is a size-24 starting battery for the (outboard) engine. This CAN be used for the house circuits in an emergency (which would be a complete failure of BOTH house batteries at once; so how common is that?). The motor's alternator (tiny as it is) CAN charge the house bank if necessary. Also the 115-vac charger CAN be used to charge the engine battery (as a second bank)-- but otherwise in all normal cases the engine (starting) bank is entirely separate from the house (deep-cycle) bank.
(If the engine starting battery fails I have to pull-start the motor. That's good enough as a fail-safe as it's not that difficult and a cheap solution.)
So it comes to this-- never should two different kinds of battery be combined in one bank; never should multiple batteries of the same bank be separated. Unless you have money (and boat) to burn.
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