How to use and charge two separate batteries

[simonfraser]

I have two lead batteries, same type.
KAD44EDC
After tightening the battery terminals each battery can now start the KAD. However there is bound to be more stress on a single battery, so I connect them both for starting. I have to leave them both connected whilst the engine is running else they don't both charge.

I guess the idea then is to switch one off in case I run the lot down and cant start the engine any more ?
But other than that, why not leave them both on, or connect them both in parallel and use them as one bigger unit ?

 

[Tranona]

Rather depends on what system you have. Useful to have two independent start batteries, one for each engine and a separate house bank charged through a VSR which is automatic. Charges the start batteries first then the house bank. Also useful to be able to parallel the house bank to the start for emergencies. If only used for engine start batteries will last a long time as although the demand is high for start the draw in amps is low, so the batteries recharge very quickly and are fully charged most of the time.

 

[BartW]

I assume you have only one engine ?

I would use one batt for engine start, and the other for house,
and interconnect the two batt's with a Victron Cyrix,

so when the alternator or a battery charger on one of the batt's raises the voltage above 13V, the cyrix will activate, and batt's will interconnect. (and both charge)
when there is no charge, (both batt at approx 12V,) the cyrix de-activates, and you can not drain the engine batt with house consumption.

there is also a safety function, the cyrix won't activate if one of the batt's is below a certain voltage (11V IIRC)

 

[simonfraser]

Tnx, yes one engine.
Does the Cyrex work both ways ?

 

[BartW]

Does the Cyrex work both ways ?

Yes it does,
Basically it is a powerfully relay, and a micro controllor looking at voltages...