Mix AGM and traditional Lead Acid??

[SteveS]

So one of the batteries on the Hedgehog (100 series) refuses to charge sufficiently to get the little green indicator to 'light' in the battery (stays black) which I'm taking to mean time to get a new battery soon. It got a bit of a beating over the summer as this is the 'leisure' battery on the split charge system (actually the offside battery).

I had in mind to replace both with Odyssey batteries but they a limited range in the mirror pairs - so I'd have to put up with 75Ah rather than 105Ah on the Numax (currently) so that seems a no-go. However, the slightly knackered 'leisure' battery is the standard config one and not the mirror image terminals.......so I thought I could put an Odyssey there at 100Ah.....just fits.

But, AGMs have a slightly different voltage.....anyone with experience of running a mixed AGM/LA battery set-up?

The split charger is an IBS

 

[Chris]

Not quite sure I can envisage your set up there Steve. There certainly aren't any safety issues mixing the batteries, but performance wise the AGM does prefer a higher charge voltage. I have a 12v start with a split that kicks in to charge the leisure batt. So I only have one cranking battery. I also have a CTEK split that charges and identical AGM battery in the boot but at 14.5. Once the alternator ramps down, the front AGM only get that typical 13.8. What I can tell you is that the two identical AGMs perform differently. I have meters watching them both and the rear one will sit and hold over 13v for weeks when not used. The front one just won't. Every month I put the mobile CTEK charger on it for a good soak and the float voltage comes back up. But I think if I didn't do that then essentially the front AGM would start to become a standard battery if you get me and probably soon fail. If your IBS kicks out a constant higher voltage then great.

People often put Optimas in the front for cranking. As I see it you get no material advantage at all in doing that on a standard vehicle.

 

[SteveS]

Thanks Chris. The IBS puts the full alternator output to the batteries (relay rather than diode switched). To do this it links the start and leisure battery together - hence my question about running the two battery technologies. Interesting about your AGM characteristics. Think I might just go for it. What's the worst that can happen.......only a battery fire - ha ha. Seriously I will give the guys at odyssey a ring. There must be plenty of installs with an AGM leisure battery across a traditional LA - I just wanted to know if it affects longevity or performance of either type. The resistance and battery voltage difference will create current flows across the two but with the alternator driving them I can't see those will be important