Charging multiple batteries

Submitted: Saturday, Jun 03, 2017 at 18:46
ThreadID: 135009 Views:2318 Replies:4 FollowUps:1
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I am going overseas for 3 months shortly and will be leaving 2 vehicles locked in the garage.

Can I connect a smart charger to one vehicle battery and then use jumper leads to the other vehicle to keep both batteries charged?

I have found both to go flat if I leave for a long time, I guess security systems etc are still draining power.
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Reply By: Athol W1 - Saturday, Jun 03, 2017 at 19:23

Saturday, Jun 03, 2017 at 19:23
Yes, just ensure that there is adequate safety measures in place so as to minimise any risk of short circuit if any lead comes adrift. I would be more inclined to make up a twin 4mm lead with eye terminals on each end and secure to appropriate points on each car.
You would be surprised at the parasitic loads that exist in the modern motor vehicles, make sure that they are both locked even whilst in the locked garage, and you may have to 'take care or' any sensor for the bonnet being opened.

Typically caravans have multiple batteries but only one mains voltage charger.
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Follow Up By: HKB Electronics - Sunday, Jun 04, 2017 at 10:59

Sunday, Jun 04, 2017 at 10:59
This will be another where I get into more trouble for over complicating it,it is ok assuming both have similar types of batteries.

As more models become available with full calcium batteries and charging systems one needs to ensure that you don't use the calcium setting if one car has a full calcium battery and the other a lead acid as the calcium algorithm charges to a lot higher voltage.

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Reply By: Dean K3 - Wednesday, Jun 07, 2017 at 19:37

Wednesday, Jun 07, 2017 at 19:37
Old school disconnect batteries from vehicle and keep a maintenance charger on them - ie two chargers one per vehicle memory will be lost to radios and clock but engine management shouldn't be affected

Old man did same using a solar panel with it set for afternoon sun on cruiser and maintenance charger on the corolla - didn't really work due to parasitic current flow i just ended up driving them both about once every 2 weeks for the 3 months they were away.

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Reply By: The Bantam - Saturday, Jun 10, 2017 at 22:41

Saturday, Jun 10, 2017 at 22:41
Sorry but I simply would not leave any "smart charger" unattended for 3 months.

They can get confuesed and get into an over charge situation.

Personally my preference would be a transformer based charger with an analogue regulator.

Yes and one for each battery.

1.5 amps would probably be sufficient.

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Reply By: Allan B (Sunshine Coast) - Sunday, Jun 11, 2017 at 09:51

Sunday, Jun 11, 2017 at 09:51
You can get into serious strife with continuous long-term battery charging so care should be exercised.

The terms 'Float Charger' and 'Trickle Charger' and 'Fully Automatic Charger' are used irresponsibly and it would be easy to select a product which would harm your battery. Maybe also harm your precious car electrics.

What you need is a Float Charger or a multi-stage charger that incorporates a true float charging mode.

Projecta (a reliable product brand) offer a small & simple 900mA charger which provides a float mode. The model is AC150 and retails for about $45. Here is one Ebay source.
Another suitable product is the CTEK XS0.8 a 6-step 0.8A charger retailing for around $69. This would be my preference.

There can be problems with connecting batteries in parallel whilst charging, especially in float mode, so I would recommend using a separate charger for each battery. Also be very sure that the connection of the chargers to the battery are very reliably secure.


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