Deep cycle battery in parallel with regular battery

[budduggley]

Is it a no-no to connect a marine (deep cycle) battery in parallel with a regular, heavy duty battery? This would be for drawing power as well as charging.

 

[ezmobee]

Re: Deep cycle battery in parallel with regular battery

Someone will be along to correct me if I'm wrong but I'm pretty sure there is no issue with that and it is done all the time. A starting battery and a deep cycle hooked up via a [1,2,or Both] selector switch is a common set up.

 

[waterinthefuel]

Re: Deep cycle battery in parallel with regular battery

Voltage is all that matters. Amp capacity is irrelevant.

It's fine.

 

[JB]

Re: Deep cycle battery in parallel with regular battery

Bad idea. Here is why:

All batteries have internal impedance. That is why, for example, your starting battery drops to, let's say, 10 volts while starting. The current (very high) is actually dropping 2.6 volts inside the battery.

Now if you have 2 batteries in parallel that do not have the same, or very close, internal impedance the current supplied by them will differ. . .whatever amount of current needed to drop the same voltage in each. That could be bad news.

Use the "both" position of your switch for charging only.

 

[Outsider]

Re: Deep cycle battery in parallel with regular battery

A starting battery and a deep cycle hooked up via a [1,2,or Both] selector switch is a common set up.

It is common, but only the 'Both' position is a parallel. Conventional wisdom is do not parallel different battery types, only those of similar type and size ...

 

[MTboatguy]

Re: Deep cycle battery in parallel with regular battery

When I was in the RV business, we would only hook up two of the same identical batteries, hooking normal batteries this way with deep cycles are a bad idea, it will cause a loss of life of both batteries due to the differences in capacities and charge rates.