Replacing Batteries

[snorkmaiden]

Any truth in the notion that when replacing the weaker of 2 lead acid batteries I should replace both, even if the second one seems in relatively good nick? I think we are talking 5 / 4 years, nothing fancy, just 110 AH truck type batteries.

 

[savageseadog]

If you're going blue water, cruising for months or working isolated anchorages probably replace both. Otherwise have the batteries tested to confirm condition and replace when necessary. "Truck type" batteries are not suitable for deep discharge applications if that's what you have. Best to have a dedicated motor battery for starting the engine and a deep discharge one for house.

 

[CAPTAIN FANTASTIC]

You only replace the failed battery, however, if both batteries were installed at the same time and are same type, I suggest that both batteries are replaced on the basis that the other one is likely to fail in the near future.

 

[RichardS]

Is there some concern that if one of the batteries is old then it will not be charging as easily or fully so the new, stronger battery connected in parallel will start charging the weaker battery when they are disconnected from the charger and this sets up some sort of oscillation which ultimately reduces both batteries?

I'm sure I read this somewhere once.

Richard

 

[aluijten]

Is there some concern that if one of the batteries is old then it will not be charging as easily or fully so the new, stronger battery connected in parallel will start charging the weaker battery when they are disconnected from the charger and this sets up some sort of oscillation which ultimately reduces both batteries?

I'm sure I read this somewhere once.

Richard

Typically the old battery has an higher internal resistance. That leads to differences in charging state between the two. Also current drains are taken for more then 50% from the fresh battery. That causes faster deterioration on the new battery shortening it's useful life while not prolonging the old battery's life. Renew them all or don't renew at all.

 

[William_H]

Batteries hard wired in parallel to increase capacity are perhaps more of a concern when miss matched. However if OP is talking 2 batteries each isloated from the other. 2 batteries for redundancy connected by a 1,2,both,off switch then miss match will not really matter as they are only in parallel for charging. However do be on the lookout for possible charging problems. Any doubt and charge them individually. Cos that bad one is sure to die sometime. good luck olewill