Parasitic parallel battery drain?

[NickRobinson]

Bit of a repost here from my post on the 1 or 2 batteries post as it is a fairly common setup

Below just refers to house batts.. the start is separate (there may need to be another thread about mixing diode splitters, Sterlings and 1/2/both switches and VSRs later-

I have a shiny new 110 Ah and a tired but functioning 85 Ah (c. half capacity now). I could parallel them but (yes I would insert an ammeter and have a look-see) would there be a significant permanent drain from the new to the old/er ?

So- to parallel unmatched batteries- a significant problem or no?

N

 

[Chris_Robb]

Bit of a repost here from my post on the 1 or 2 batteries post as it is a fairly common setup

Below just refers to house batts.. the start is separate (there may need to be another thread about mixing diode splitters, Sterlings and 1/2/both switches and VSRs later-

I have a shiny new 110 Ah and a tired but functioning 85 Ah (c. half capacity now). I could parallel them but (yes I would insert an ammeter and have a look-see) would there be a significant permanent drain from the new to the old/er ?

So- to parallel unmatched batteries- a significant problem or no?

N

The purist will say that you should only link matched batteries - ie same size, same make, same age. It is however a sliding scale of acceptability. I personally would only connect batteries of a similar size, but would allow a bit on age if the older battery was conceived to be still a gooden.

BUT

To connect to very different batteries when one is known to be way down, is at the other end of the sliding scale. You will probably find that your old battery has but a year to go - so just get another to match.

By connecting your new battery to this old one, you will effectively bring down the level of the good battery to the lowest comment denominator, so engineering an early demise for the new one.

If you have not already got battery monitors, get one - the best value for money (IMHO) is the NASA BM1, which is simple to fit, shows not only what you are using so that you learn a lot about the consumption of each item, but also the charge rate in AMPs and the battery voltage on the house bank.

 

[vyv_cox]

I agree with Chris' sensible summary. I converted my domestic battery bank of two batteries, around three years old, to a bank of three by adding the starter battery, about five years old but little used. All were 110 Ah leisure types. The combined bank gave me around three more years with no problems.