Wiring Batteries in Series or Parallel
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Did you know whenever you connect two or more batteries together in series or parallel applications, those batteries should always be identical in age, size and type? To understand this concept, think of each battery as a pool of water, filled by a common hose.
AGE
As batteries age and/or are used, their internal resistance increases, which makes it harder for them to accept and deliver current. That effectively makes an older battery act like a larger battery when trying to charge batteries together. The higher internal resistance means it will take longer to get that older battery fully charged, while the newer battery (or batteries) may get fully charged much faster and then overcharged, before the older battery reaches a full state of charge.
SIZE
Using the pool scenario again, if two batteries of dissimilar sizes are connected to a common source of electricity, that smaller battery can get overcharged before the larger battery reaches a full state of charge, just like a hot tub would overflow before a swimming pool ever fills up. If charging stops before the larger battery gets past 12.4 volts, sulfation can form in the plates of the larger battery, further increasing internal resistance.
TYPE
Lead-acid batteries that uses recycled lead or tombstone welds to connect cells may not accept or deliver current at the same rate as lead-acid batteries that use 99.99% pure virgin lead or robust cast straps to connect cells. Lithium batteries may accept current far faster than any type of lead-acid battery. Mixing these types of batteries together in series or parallel applications can again lead to one battery being constantly overcharged, while others are undercharged.
Some of the most common parallel and series applications include diesel trucks with two batteries and trolling motors with two or three batteries. If one battery fails in those applications and needs to be replaced, all the batteries in that application should be replaced. That doesn't mean all the old batteries need to be recycled, but the remaining good batteries should probably be used in other applications, where a smaller bank could still be identical in age, size and type or where a battery can be used by itself. Don't forget, you can always buy factory-direct here.
AGE
As batteries age and/or are used, their internal resistance increases, which makes it harder for them to accept and deliver current. That effectively makes an older battery act like a larger battery when trying to charge batteries together. The higher internal resistance means it will take longer to get that older battery fully charged, while the newer battery (or batteries) may get fully charged much faster and then overcharged, before the older battery reaches a full state of charge.
SIZE
Using the pool scenario again, if two batteries of dissimilar sizes are connected to a common source of electricity, that smaller battery can get overcharged before the larger battery reaches a full state of charge, just like a hot tub would overflow before a swimming pool ever fills up. If charging stops before the larger battery gets past 12.4 volts, sulfation can form in the plates of the larger battery, further increasing internal resistance.
TYPE
Lead-acid batteries that uses recycled lead or tombstone welds to connect cells may not accept or deliver current at the same rate as lead-acid batteries that use 99.99% pure virgin lead or robust cast straps to connect cells. Lithium batteries may accept current far faster than any type of lead-acid battery. Mixing these types of batteries together in series or parallel applications can again lead to one battery being constantly overcharged, while others are undercharged.
Some of the most common parallel and series applications include diesel trucks with two batteries and trolling motors with two or three batteries. If one battery fails in those applications and needs to be replaced, all the batteries in that application should be replaced. That doesn't mean all the old batteries need to be recycled, but the remaining good batteries should probably be used in other applications, where a smaller bank could still be identical in age, size and type or where a battery can be used by itself. Don't forget, you can always buy factory-direct here.