I'm about to add batteries to my house bank. In the location where I plan to put these I can put two group 31's and one group 27. The 27 fits in the same existing box along with the starting battery so it's nice to fill up that space instead of leaving it empty which is why I'm mixing different battery sizes. If I connect all these in parallel for the house bank is there any problem mixing sizes? I plan to get them all new. Thanks, Bob
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not advisable
Bob It's generally not as good idea to mix battery types. The smaller Gr27 is likely not the same capacity as the 31s and would therefore affect the charger differently. The 27 will loss a proportionately larger percent of it's capacity than the larger batteries and when you recharge, it will affect the charge rate of the bank potentially causing overcharging. When they are all new and fully charged, it's irrelevant, however, the first time you draw them down, the trouble begins as they don't recharge equally. Frankly, the battery box issue isn't a good reason to do it. If you are repacing all batteries, you might want to consider a set of 6V batteries which lots of the so-called experts consider the best setup. Don
Bob It's generally not as good idea to mix battery types. The smaller Gr27 is likely not the same capacity as the 31s and would therefore affect the charger differently. The 27 will loss a proportionately larger percent of it's capacity than the larger batteries and when you recharge, it will affect the charge rate of the bank potentially causing overcharging. When they are all new and fully charged, it's irrelevant, however, the first time you draw them down, the trouble begins as they don't recharge equally. Frankly, the battery box issue isn't a good reason to do it. If you are repacing all batteries, you might want to consider a set of 6V batteries which lots of the so-called experts consider the best setup. Don
Just Do It
Try to use the same make of battery and the same technology. ie. Flooded, Maintenance free, AGM etc. Buy them all from the same maker etc. You may not get the optimum performance out of all the batteries BUT you WILL increase the overall capacity by approximately the capacity of the additional batteries. I doubt you will damage anything and, of course, it is best to use a multi stage charger to ensure at least 95% charge. The charger will hardly notice the difference between #27 and #31. I added two smaller 85 Ah batteries to my existing 105 Ah ones about 5 years ago and the system handled it perfectly.
Try to use the same make of battery and the same technology. ie. Flooded, Maintenance free, AGM etc. Buy them all from the same maker etc. You may not get the optimum performance out of all the batteries BUT you WILL increase the overall capacity by approximately the capacity of the additional batteries. I doubt you will damage anything and, of course, it is best to use a multi stage charger to ensure at least 95% charge. The charger will hardly notice the difference between #27 and #31. I added two smaller 85 Ah batteries to my existing 105 Ah ones about 5 years ago and the system handled it perfectly.
Don't confuse battery types with battery sizes
My experience has been that paralleling different size batteries is fine as long as they're the same type (gel, AGM, lead-acid.) I've got a house bank that is 4xgrp27 and one grp 24 that are two years old and live together happily. In fact, I just did an equalize and hygrometer check last weekend and every cell is still at 1.275. I'm no EE but I belive that the different size batteries DO discharge and charge proportionally according to their size and capacity provided all the cells are the same type/age/condition. The cells will then move to the same charge/discharge states together and the charger won't "see" them seperately. It's when you get a bad cell that the charger runs according to that "least common denominator" (lower voltage) and boils out the rest. Anyway, my personal experiences have bourne out my little half-baked theory though your mileage may vary. Naturally, you guys are always free to tell me I'm full of crap
(You'd be right of course.)
My experience has been that paralleling different size batteries is fine as long as they're the same type (gel, AGM, lead-acid.) I've got a house bank that is 4xgrp27 and one grp 24 that are two years old and live together happily. In fact, I just did an equalize and hygrometer check last weekend and every cell is still at 1.275. I'm no EE but I belive that the different size batteries DO discharge and charge proportionally according to their size and capacity provided all the cells are the same type/age/condition. The cells will then move to the same charge/discharge states together and the charger won't "see" them seperately. It's when you get a bad cell that the charger runs according to that "least common denominator" (lower voltage) and boils out the rest. Anyway, my personal experiences have bourne out my little half-baked theory though your mileage may vary. Naturally, you guys are always free to tell me I'm full of crap
(You'd be right of course.)Expain the theory of 6volt
Could someone please help me understand how to use 6volt and why that is better. would two 6volt wired in sieries be equal to 12volt? Do 6volt batteries hold a charge longer? Do 6 volt batteries last longer? What is the cost-benefit ratio? Thanks.
Could someone please help me understand how to use 6volt and why that is better. would two 6volt wired in sieries be equal to 12volt? Do 6volt batteries hold a charge longer? Do 6 volt batteries last longer? What is the cost-benefit ratio? Thanks.
6V cost and weight
Hi Liam - The benefits of 6V batteries is that the are relatively inexpensive and are easier to move (i.e. install and replace) since individually they are lighter in weight. Hope this helps! Trevor
Hi Liam - The benefits of 6V batteries is that the are relatively inexpensive and are easier to move (i.e. install and replace) since individually they are lighter in weight. Hope this helps! Trevor
6 V vs. 12 V
Liam, Six volt batteries have three cells while 12 volt batteries have 6. Each cell contributes about 2.3 volts per cell to the overall voltage of the battery. Three big cells gives you more lead, and hense more amp hours, than 12 volts for the same size battery. The six volt batteries tend to be better built than their 12 volt cousins as well. That being said, I use 4 group 31 lead-acid 12 volt batteries arrayed in two banks giving me about 420 total amp hours. I pay about $70 for these batteries and I get 6 or 7 years out of them. If I head to the islands, I'll upgrade to good six volt units, but for now, cheap 12 volt batteries make more sence to me. Fair winds, Steve S/V Aurelia
Liam, Six volt batteries have three cells while 12 volt batteries have 6. Each cell contributes about 2.3 volts per cell to the overall voltage of the battery. Three big cells gives you more lead, and hense more amp hours, than 12 volts for the same size battery. The six volt batteries tend to be better built than their 12 volt cousins as well. That being said, I use 4 group 31 lead-acid 12 volt batteries arrayed in two banks giving me about 420 total amp hours. I pay about $70 for these batteries and I get 6 or 7 years out of them. If I head to the islands, I'll upgrade to good six volt units, but for now, cheap 12 volt batteries make more sence to me. Fair winds, Steve S/V Aurelia
6 volt batteries
For some reason, the 6 Volt GOLF CART batteries ( deep cycle ) are of a much higher quality than the marine deep cycly. Probably because the competition for the Golf Cart batteries is much greater and the use is much more demanding. When i had an electric fork lift, golf cart batteries were the only recommened ones to use. Marine batteries are of a different breed, which i'm sure is actually legislated as to when you can call them marine grade. Marine grade batteries have more rigorous testing for safety in different environments such as diesel fuel, gasoline and oil leaks as well as salt water corrosion on the terminals. While marine batteries try to satisy the above, golf cart batteries are more performance oriented. I use golf cart batteries and will continue to use them. I dont know of anyone that ever has had a problem with them. Now for your original question..can you mix batteries? The answer is NO. As some have stated earlier on this post, the problem lies with the 'charging ' aspect. When you put batteries in the same bank, which you will have to, they will not charge at the same rate which means some will over charge and some will under charge. Also the weaker batteries will pull down the better ones, that is also why it is recommended to always replace the entire bank at the same time rather than only one battery at a time.
For some reason, the 6 Volt GOLF CART batteries ( deep cycle ) are of a much higher quality than the marine deep cycly. Probably because the competition for the Golf Cart batteries is much greater and the use is much more demanding. When i had an electric fork lift, golf cart batteries were the only recommened ones to use. Marine batteries are of a different breed, which i'm sure is actually legislated as to when you can call them marine grade. Marine grade batteries have more rigorous testing for safety in different environments such as diesel fuel, gasoline and oil leaks as well as salt water corrosion on the terminals. While marine batteries try to satisy the above, golf cart batteries are more performance oriented. I use golf cart batteries and will continue to use them. I dont know of anyone that ever has had a problem with them. Now for your original question..can you mix batteries? The answer is NO. As some have stated earlier on this post, the problem lies with the 'charging ' aspect. When you put batteries in the same bank, which you will have to, they will not charge at the same rate which means some will over charge and some will under charge. Also the weaker batteries will pull down the better ones, that is also why it is recommended to always replace the entire bank at the same time rather than only one battery at a time.
Mixing Batteries
Age difference is the big factor when mixing batteries of the same type. Different sizes may have a problem when charging. Consult Nigel Calder's book on boat systems. He may have your answer.
Age difference is the big factor when mixing batteries of the same type. Different sizes may have a problem when charging. Consult Nigel Calder's book on boat systems. He may have your answer.
Don't mix
Because they are in parallel the voltage for both battery is is equal. Assuming the same internal resistance of the batteries, the current (amps) will be equal as well. So the smaller battery will discharge more quickly relative to its total capacity. The rule of thumb is that you don't want to discharge a battery much below 50%. The smaller battery will reach that level more quickly and therefore wear out more quickly. That's the theory at least, no idea if in practice other factors (e.g. maintenance, manufacturing quality, bad luck) aren't more important.
Because they are in parallel the voltage for both battery is is equal. Assuming the same internal resistance of the batteries, the current (amps) will be equal as well. So the smaller battery will discharge more quickly relative to its total capacity. The rule of thumb is that you don't want to discharge a battery much below 50%. The smaller battery will reach that level more quickly and therefore wear out more quickly. That's the theory at least, no idea if in practice other factors (e.g. maintenance, manufacturing quality, bad luck) aren't more important.
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