Full River battery charging

[Rob_Webb]

Recently I replaced my house bank with 4x 105Ah Full River AGM new batts. The product spec says:
1. Bulk charge at 14.7v
2. Absorption charge at 14.7v
3. Float charge at 13.7v
Which seems higher than most batts but hey that's the product spec so that's what we should do, right?
Then soon afterwards I replace my shore power battery charge with a new Victron Phoenix unit that can be configured for exactly this charging profile (which we do). But then we notice the float charge dropping from 13.7v to 13.2v frequently. The reason is that the Victron charger has a 'Storage Mode' which reduces float to 13.2v after 24 hrs of no battery activity (e.g,. when left on the marina) to avoid excessive charging and gassing etc. This sounds plausible, right? But who to go with - 13.2v Victron (experts in battery charging) or 13.7v Full River (the actual manufacturer).

My instinct is to go with Full River and switch off the Victron 'Storage Mode' so it keeps float at 13.7v. I do know that whilst 0.5v doesn't sound much, in the longer term it can make a huge difference to battery life if you get it wrong either too high or too low.

Anyone else faced this scenario?

 

[PaulRainbow]

Let the Victron have its way, no need for your batteries to sit at 13.7v 24/7 when not in use.

 

[TernVI]

When people write schedules for bulk/absorption/float and all that, they are often making assumptions about daily use cycles.
In industry, a lot of batteries are used like that.
If you store a battery with a 13.7V float charge long term, with no discharges, you may find it dries up.

 

[[70521]]

My float charge is 13.4 volts and from what I've read, about a hundred conflicting sources, float charge can be => 13.2 =< 13.7 volts.

 

[Zing]

Check your battery manual. The optimum float charge varies slightly between lead acid battery technologies and it depends on temperature also, but it is in that area. I set my charger to 13.85v in winter, 13.7 in summer. A constant voltage trickle charge at the correct voltage is recommended as the best method of keeping the batteries in storage for maximising life by the maker of my AGMs (Enersys) and they know a thing about batteries.

 

[Rob_Webb]

There is an added complication I didn’t mention earlier.

2yrs ago (on my previous boat) I had the identical AGM Full River batteries installed and after only 6 months they died. After testing by the NZ importer / distributor the reason was found that the professional marine electricians who installed them made the mistake of setting my charger to AGM on the assumption that all AGMs are the same - without checking the actual product spec.

And so the AGM setting produced a charging profile of Bulk 14.4v / Absorption 13.8v / Float 13.2v. And because this was under the 14.7 / 14.7 / 13.7v manufacturer’s recommendation it killed the batts (replaced under warranty).

But I don’t know if the thing that killed them was the Bulk and Absorption voltages being too low or the Float voltage (or all 3).

Hence my dilemma. I know my new setup is giving correct Bulk and Absorption of 14.7v and it’s only the Float that is dropping from the recommended 13.7v to 13.2v after 24hrs. And I don’t know if that is a repeat problem waiting to happen again or not.
Any battery technicians out there?

 

[[70521]]

Your best course of action is to contact the technical department of the manufacturer.

 

[BabaYaga]

If your new batteries are anything like mine, they likely have a very low self discharge and an excellent shelf life and so could sit happily for many months with no charge at all.
To me it seems unlikely that 13.7 v and no charge would both be OK while 13.2 would be harmful.

 

[Zing]

I’m not a qualified battery technician, but I have read a lot of manuals. Those voltages would not have destroyed your battery, barely harmed them, but it does depend on how long they were at absorption or bulk. It shouldn’t be for days. I think something else went wrong.