Second battery ... replace the first, too?

dgadee

dgadee

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There seems to be a suggestion that if I add a second domestic battery I should install two identical new batteries rather than just a new similar battery to the one already installed.

Is that necessary? Would one failing battery affect the other if they are in parallel?
 
dgadee said:
There seems to be a suggestion that if I add a second domestic battery I should install two identical new batteries rather than just a new similar battery to the one already installed.

Is that necessary? Would one failing battery affect the other if they are in parallel?
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Not absolutely necessary.. but the two must be the same type ie have the same charging characteristics.
BUT
It would be folly IMHO to put a brand new battery in parallel with a nearly knackered old one ... they'd probably behave differently when being charged and if the old one is not holding its charge well it'll pull the new one down with it probably. The bank may well not be any better than the failing battery.
 
VicS said:
Not absolutely necessary.. but the two must be the same type ie have the same charging characteristics.
BUT
It would be folly IMHO to put a brand new battery in parallel with a nearly knackered old one ... they'd probably behave differently when being charged and if the old one is not holding its charge well it'll pull the new one down with it probably. The bank may well not be any better than the failing battery.
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First battery is fine - not really keen to just dump it. I am installing a fridge unit in the cool box and think a second battery probably needed.
 
dgadee said:
First battery is fine - not really keen to just dump it. I am installing a fridge unit in the cool box and think a second battery probably needed.
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If the existing is good then keep it!
You could consider a three battery system with VSR charge splitting. Keeping one exclusively for the fridge..
 
Batteries in parallel

You can try the batteries in parallel however I would suggest you make it convenient to disconnect either battery +ves from the circuit so that at any hint of problem you can separate the 2 and sort out if the old one is cream crackered. olewill
 
I have a friend with an electric boat. 16 batteries at £90 each would be a lot to pay for.
He just replaces ones that go down with identical ones.
 
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When I asked them Trojan "recommended" rather firmly that a battery that was over 12 months old should not be paired with a new one because the charge profiles would be different and one would dominate(?) If they were trying to get me to buy three new batteries they failed, I'm learning to be content with two (and I have to say they do keep going despite all the mistreatment I give them).

David Berry
 
OP here.

My system is a Sterling Alternator to Battery charger with two outputs - to a domestic and to a start battery. When I add the solar panel it will be controlled by an mppt controller, mainly for charging the domestic battery(ies) but I wonder about if topping up the starter battery if the domestic batteries are full is possible.

Could I sent this mppt output to the Alternator to Battery charger? Or what?
 
dgadee said:
I wonder about if topping up the starter battery if the domestic batteries are full is possible...
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Not really. There are a lot of claims for various devices that will sense when your battery is full. The only reliable way is to measure the SG, or measure the charge current over time. A VSR will sense when the voltage hits a predetermined point, but this is pretty much meaningless while the charge current is still flowing.
 
dgadee said:
OP here.

My system is a Sterling Alternator to Battery charger with two outputs - to a domestic and to a start battery. When I add the solar panel it will be controlled by an mppt controller, mainly for charging the domestic battery(ies) but I wonder about if topping up the starter battery if the domestic batteries are full is possible.

Could I sent this mppt output to the Alternator to Battery charger? Or what?
Click to expand...

I dont think you can feed the AB charger from the MPPT controller

use the AB charger for it intended purpose namely controlling charging from the alternator.

Let the MPPT controller do what it is intended to do, namely optimise the performance of the solar panel.


I am not sure that a VSR to split the output from the solar system would be a good idea either with an AB charger fitted.!
 
dgadee said:
OP here.

My system is a Sterling Alternator to Battery charger with two outputs - to a domestic and to a start battery. When I add the solar panel it will be controlled by an mppt controller, mainly for charging the domestic battery(ies) but I wonder about if topping up the starter battery if the domestic batteries are full is possible.

Could I sent this mppt output to the Alternator to Battery charger? Or what?
Click to expand...

Not much point really. Your starter doesn't use many Ah for starting, and it is soon replenished even if you only run the engine for a short while.

Admittedly, if the battery sits unused for several months, it will self discharge to a degree, but not much more than a couple of percent a month, unless it's shot.
 
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