John replied:

How does a good dual battery system get to be dead from use unless you have ben sitting for a week or so without driving/starting the engine ?

If you have a problem why not contact Piranha direct??

john

Joe replied:

Tony,

John is right, the best way to charge the batery would be to drive the truck and let the charging system do the work.

But, if you need to charge it while stationery then conventional wisdom dictates that you should disconnect the battery cables. It is always wise to try to isolate your electrical system (even the relatively simple system in a Tojo diesel) from the potential impact of spies etc from an external charging system.

Joe

Ray replied:

Hi,

This is a really interesting subject and one that many people are a little unsure of and for good reason even some of the professional advice is flawed. In general the charging system of most if not all vechiles is not designed to fully charge dead flat batteries, it's role is to top up batteries after starting and running very small numbers of aux's. The demand we place on the charging system in our situations is very high. I spent a long time researching this area before I decided to move to a 12v fridge with three batteries in the car. The more informed you become the more chance of having few hassles and longer life of your batteries. If you simply do the maths you'll find that for a standard charging system to fully charge a flat battery your would need to drive for days, and even then it may only be surfaced charged. Don't think that because you have an 80amp altenator that you get any where near that to the battery depending on the driving situation and the instalation you may be flat out getting 10% of that to the second battery. I won't go on further as the info I found out could take up a couple of pages. The best bet for anyone using dual battery systems is to speak with your local auto electrician in general they will be able to give you more than enough info.

PS I don't disconnect my batteries when charging externally but I've no doubt it would be safer as suggested by the previous reply.

Nigel Gorry replied:

I have to disagree with Joe and John. A car alternator is rarely capable of fully recharging a battery. This is even more true of a second battery that only charges in parallel with the main battery (independant charge systems like the more expensive Rotronics units help in that case). The best advice I was ever given was to put the battery on a mains charger once a month. While it's probably safer to remove the battery from the vehicle, I often charge the aux battery while it's still connected to the car. Just make sure all loads are turned off. As long as your dual battery system isolates the aux battery from the main then there will no problems with spikes affecting your car's electronics as there should be no connection when the car is not running.