SLA Battery charger

Submitted: Tuesday, Apr 18, 2006 at 12:05
ThreadID: 32987 Views:6294 Replies:9 FollowUps:4
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Battery Gurus,

Can I use my car battery charger to charge 7ah sealed lead acid batteries? I have one of those Arlec cheapies.

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Reply By: Member - Roachie (SA) - Tuesday, Apr 18, 2006 at 12:13

Tuesday, Apr 18, 2006 at 12:13
I would think that it would be okay, but you wouldn't want to be leaving it on the charger for too long. If it's a 4amp charger, I reckon 2 hours would be enough to charge a fully discharged 7 amp battery.

I have a 7a/h battery kit (ie: in a zipped bag, with cigi plug at one end etc) and I keep it plugged into a cigi socket in the battery compartment of my Ultimate Camper. That way it is always ready to use for our "street light" around the camp fire. ("Street Light" is the term we use for a custom-made heavy peg that we drive into the ground which has a piece of water pipe welded to the side. The i.d. of that water pipe is just large enough to suit a tent pole. Then we have another custom-made gizmo that slips over the top of the tent pole which is designed to hold the handle of a Versa lite or similar variation. The little 7a/h battery kit sits on the ground at the base of the pole and runs the street light for around 6 hours or so.


AnswerID: 167545

Follow Up By: Leroy - Tuesday, Apr 18, 2006 at 12:17

Tuesday, Apr 18, 2006 at 12:17
That's exactly what I'm going to use this batter for. I actually modified the charger with a kit from *ick Smith that prevent's overcharging of the batt. incase I forgot about it.

FollowupID: 422740

Reply By: Member - Phil G (SA) - Tuesday, Apr 18, 2006 at 15:42

Tuesday, Apr 18, 2006 at 15:42

#1 Your Arlec is probably unregulated and open circuit voltage might be about 16 volts which will damage a small SLA battery. If you have fitted a regulator kit, then it might be OK.

#2 Your 7Ah battery will not like to be charged at more than 1 amp (should state this on the side) - I think your Arlec will want to put about 2.5 amps into it unless you've regulated it.

I have used these batteries for donkeys years. I charge them at home by connecting them overnight to a regulated 13.8 volt power supply. I recharge them in the car but hooking them up to the second battery via a relay which is energised only when the motor is running (ie relay coil is connected to IGN power). So they are only recharged while driving - and they get recharged at the vehicle's regulated 14.2 volts or less. I have had no issues with longevity - my batteries have lasted many years and were purchased second-hand originally. I recharge them frequently, trying not to deep discharge them and while away they live in the vehicle hooked up.

AnswerID: 167577

Reply By: TerraFirma - Tuesday, Apr 18, 2006 at 16:04

Tuesday, Apr 18, 2006 at 16:04
These chargers are pretty dumb in the overall scheme of things so be careful, a 7ah battery would charge in around 1 hour by a 6amp battery charger, pretty much what the cheapies are I think, 5 or 6 amps. Any longer than that and you could damage the battery. Even 30 minutes would be fine if the battery is not completely dead
AnswerID: 167581

Follow Up By: Member - Phil G (SA) - Wednesday, Apr 19, 2006 at 09:15

Wednesday, Apr 19, 2006 at 09:15
Terrafirma, it doesn't quite work like that.

The battery charger supplies a voltage, but the battery itself determines how much charge (amps) are taken. So a fully charged battery will take very little from a 6amp charger, while a discharged battery will take more. And a big battery will take more current than a little battery. Also its pretty hard to get a "6amp" charger to deliver more than about 4 amps into most batteries.

The only think that will damage the battery is a charging voltage that is unregulated (too high).
FollowupID: 422963

Reply By: Member - Oldplodder (QLD) - Tuesday, Apr 18, 2006 at 17:02

Tuesday, Apr 18, 2006 at 17:02
I have 2 15amp/hour SLAs for the same purpose, to run a small light around the camp where I need it.
Bought them from Jaycar.
Jaycar recommend a maximum of a 1.5amp/12.8 volt charging current.
They also tried to sell me a solar cell for $200.00 plus to charge them, as they thought I would fry the SLAs charging them off the cigarete lighter.

Bought a cheap solar cell regulator that puts out 1.5amp and have it hooked up to the 2nd 12v N70ZZ battery under the bonnet. Takes about 3 to 4 hours to recharge a battery.
AnswerID: 167593

Reply By: Arkay - Tuesday, Apr 18, 2006 at 17:21

Tuesday, Apr 18, 2006 at 17:21
As you say you are going to use the 7ah sla battery for camp lighting. The move these days is to LED lights instead of fluros as the equivalent uses 5 to 10 times less battery. There are quite a few options coming on the market right now including a 12v circular "trouble light" (aboiut 8 LEDs) with alternative red LEDs flashing and cig lighter plug (or rip the plug off & attach direct to battery). This item $16.95 from auto parts shop. There are also some "strip" emergency type lights with multiples of LEDS but these are a fair bit more expensive ($50 or so) and some are only attached to internal small capacity rechargeable batteries, rather than running direct off 7ah or car battery.
What I did was to get a halogen table lamp (or behind-the-bed on-the-wall with switch halogen base) that TAKES A MR16 HALOGEN GLOBE. Then I replaced the halogen globe with a 12v MR16 multiple LED clusterfrom Hybralec Industries Ph. 03-9761-6780 (they have other style replacement LEDs too (see, and attached the necessary wiring for MY 7ah battery. This gets over the slightly poorer light produced by LEDs (actually your eyes soon get used to LEDs once it gets dark). Get 5-10 evenings out of the battery now.
Also consider a cheap LED garden light ($6 or so). charges up free during the day, looks ziggy & guides you to your camper/tent early evening. Turn it upside down, solar panel downon the benchtop or wherever when you go to sleen & you get adequate light in the middle of the night if you have to get up for some reason or other (i.e. if you are old like us).
Actually if I knew how I'd copy this all as a new post in the forum (can't be bothered re-typing it all). Enjoy! de Rob.
AnswerID: 167599

Reply By: noddy - Tuesday, Apr 18, 2006 at 17:32

Tuesday, Apr 18, 2006 at 17:32
Hey Leroy,

I have about a dozen of these at home at the moment :) EX UPS

Come see me if u want some.

I use a little batteryfighter 1.25 amp ( 3 or 4 stage ??? ) to charge my smaller batteries.

cost about $60 from dick smith

AnswerID: 167603

Follow Up By: Leroy - Tuesday, Apr 18, 2006 at 19:22

Tuesday, Apr 18, 2006 at 19:22
I already have 4 ex UPS also. Thanks all the same.

FollowupID: 422830

Reply By: Mike Harding - Tuesday, Apr 18, 2006 at 19:09

Tuesday, Apr 18, 2006 at 19:09
Your Arlec thingie will probably push 2 or 3 amps into a flat 7Ah battery and as that battery acquires charge that charge rate will lessen to "not a lot" - yes you can but keep an eye on things and don't leave it on charge for more than three hours or so
and if the SLA starts to get warm take it off charge.

Mike Harding
AnswerID: 167629

Reply By: Leroy - Tuesday, Apr 18, 2006 at 19:25

Tuesday, Apr 18, 2006 at 19:25
Thanks guys. I have a few of these batts. so i will see how I go. If I fry one then it's not the end of the world. I think I will also look at charging in the car also.

AnswerID: 167636

Reply By: tex1972 - Wednesday, Apr 19, 2006 at 21:12

Wednesday, Apr 19, 2006 at 21:12
Site Link interesting little gizmo from dick smith
AnswerID: 167909

Follow Up By: AdrianLR (VIC) - Wednesday, Apr 19, 2006 at 22:55

Wednesday, Apr 19, 2006 at 22:55
I used this kit to run a laptop that needed a 16v supply but it doesn't work for my new one that runs off 19v because the current drops as voltage goes up.

It should be very useful for SLA charging as it will allow charging whilst the engine's off by boosting 12.6v to 13.8.
FollowupID: 423189

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