battery bank question

[bazobeleza]

My mates newish boat has three batteries, one for engine starting switched with a house bank comprising of a 70Ah battery and a 110 Ah battery linked in parallel. The house batteries have failed, and the boat has been plagued with charging problems from new.

I always believed that it was wrong to have batteries of either different capacities or types in the same bank, but this is a manufacturers installation. Can this be correct or have the builders made an errror?

 

[FullCircle]

No problem with my 80Ah +80Ah+110Ah in one bank. Thats been working for at least 2 seasons. I have a 70Ah start battery with no issues either.
The charging problems are easily measured, but I have an alternator regulator and Voltage Sensitive relays.
What I dont have is battery temperature sensing per battery, just a general probe in the house bank box.

 

[pvb]

People will tell you that a bank of batteries should comprise batteries of equal type/size/age, but the only important factor is that they should be of equal type (ie wet, AGM, gel, etc). Individual batteries in a bank accept charge according to their own needs. Size and age aren't really important (as in real life!). I'd suggest there's another reason for your mate's charging problems.

 

[William_H]

If the house batteries have failed the first thing to do is to separate the 2 batteries and test them individually. If one battery fails in a parallel set up then it will drag the other down with it.
Test the battery by charging with a known or decent amp hour approximating the rating, into it then try discharging using a car headlight or similar while monitoring voltage. Anything approximating 50% of the rated amp hour of discharge is good. A dud will either start at low voltage or drop quickly with a load.

Then if you ahve good batteries you can consider the charging problems if they remain. An amp meter is the best measure of charging. Volt meter is oK but needs interpretation. good luck olewill