Charging regime for gel batteries.

[Birvidik_Bob]

Our domestics are shot and we have the opportunity to buy four Victron deep-cycle 165 ah batteries at a good price, but I have some concerns about the possibility of them being damaged by overcharging. I read that the absorption voltage should not exceed 14.1 to 14.4 volts. (or 28.2 to 28.8 volts in our case).

On shore power this is not a problem as we have a Mastervolt charger which can be set for gel batteries. What does concern me a bit is whether the alternator could cook them as we are on the canals and use the motor for extended periods. The boat doesn't have a smart charger and the alternator has an integral regulator.

I checked by fully charging the batteries from shore power, then disconnected it and ran the engine and measured the voltage at the battery terminals. This was 28.4 volts.

What's the assembled wisdom - can I fit the gel batteries and operate without boiling them?

Thanks for any advice.

Bob

 

[Plevier]

Victron specify a float range of 13.5-13.8V and a recharge voltage in cyclic service of 14.1-14.4V, which of course will be reduced to the float voltage before the batteries are fully charged.
If your alternator is regulated at 14.2V (per 12V battery) and you are likely to run all day frequently, then I have to say yes there will be a real danger of drying them out, particularly if you go onto shore power at night so the batteries stay fully charged. Can you change the regulator or fit an external one if you really want to use these batteries?
In general (I have no specific knowledge of Victron batteries and don't know who makes them for Victron), gel batteries are much less tolerant than AGM of such conditions, i.e. more prone to drying out. Fewer and fewer firms offer gel now (other than for very low discharge rate solar installations).
If you really want deep cycle capability the answer is something like T105s, not sealed lead calcium batteries. Victron's claimed figures are not outstanding anyway.
TBH whatever the batteries you choose you might need to do something about this voltage if it's going to apply for long periods, but these gels are likely to be more sensitive than most types.
If you have flooded batteries you'll have to top them up as necessary but probably won't shorten their lives. Many more batteries die from undercharge than from overcharge.

 

[sarabande]

It's worth phoning that lovely lady at Merlin help desk

http://www.merlinequipment.com/markets/group.asp?groupid=24

They have alternator regulators that control the output according to the type of battery and the state of charge. Eg the AMS

Satisfied customer; no other affiliation.

 

[Plevier]

I don't think that will enable you to reduce the voltage will it? Isn't it meant to upgrade charging with older alternators typically set at 13.8 to 14V?