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yet another twin battery related thread - sorry

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Hi All,

sorry for yet another twin battery related thread but i could not really find exactly what i was looking for using the search facility so decided to post instead.

I'm putting in twin batteries (with x-eng relay etc) and i've got a LR volt meter. In theory the gauge should show the same reading for both batteries (both new) but is there any benefit of having both batteries wired up to the 1 volt meter via a switch? 1 battery is to replace the main existing battery while the other one will run a new fuse board to power new circuits. Do both batteries receive a charge at the same time or it is a case of it charges the main then onto the second?

Coming from modern vehicles i've found not really being able to know what going on to be a hard learning curve (been cault out with a flat battery over xmas)so i decided to add some gauges to help me see if something is not right before it goes wrong plus my 90 is often sat doing nothing for a couple of week at a time etc. My 90 was in poor shape (slowly getting better) so having a bit of a warning / info helps me.

secondly what's the best / cost effective way of safety securing both batteries? Looking in this months various LR mag's there seems to be a new twin battery tray but at £40 + i'm not sure if there is a simplier way of doing it?

thanks and apologies if the above has been covered but i could not find it.


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Quite literally 'split' charge, as oppose to 'sequential'

Your volt meter could be used to read the batteries independently when the engine is off, but as soon as you're charging, the two batteries are connected together, and so you're charging - and therefore reading the voltage of - both simultaneously.

Probably not a lot of benefit in monitoring both / switching between them, as the major concern should be how well you're charging them, and the voltage on the main battery when cranking, but if you like fitting switches or gauges, go for it!

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You could do either option with your voltmeter. Having it read from the main battery will show you that the alternator is working which is all you really need to know. Having a switch will show you ROUGHLY what each battery is doing - it will confirm that the starting battery has power, and will show you if the aux battery has been worked hard and the voltage will drop correspondingly. I'm not sure that the extra effort to wire in the switch will be worth it though - as long as the starter battery has charge, the other can be flat and it shouldn't matter.

Be careful how you wire the batteries up. I wired my last setup so that the starter battery ONLY went to the starter, and the aux battery did everything else. This meant I could leave the radio on all day and there would still be power to turn the engine. Be aware that it you simply wire auxiliary circuits to the second battery, you can still get stranded if the radio is left on etc.

My setup did mean that if the aux battery got flat, there was not enough to open the fuel solenoid or operate the starter solenoid. This was easily fixed by jumping the two batteries together. I got started on a number of occasions when I would otherwise have been caught out.

In terms of securing the batteries, I used a long piece of angle which spanned the top of the two batteries. A bolt passed through the middle of the angle into a rod that, in turn, was bolted through the bottom of the battery box with suitable reinforcement.

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Hi guys,

thanks for the prompt reply. If the gauge wont really show me much difference then i dont really see the benefit of the extra hassle to wire them both in.

Good point about the setup Simon, at the moment i've got a cut off switch fitted so i will need to think about how best to cut the power to the second battery. Can i wire both batteries through one battery cut off switch?

I think to save cash i'll explore some angle options rather then a shiny tray..



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