I have some bits laying around and need to build a 12V constantly on power source to run some circuitry. I have a sealed lead acid (SLA) battery (12V 7Ahr) and an intelligent trickle charger specifically designed for SLA batteries. The trickle charger can supply about 1A maximum charge current. The circuitry that will run constantly draws about 100mA, but very occasionally will draw 3A for 15 minutes.

Can I just run my circuitry off the SLA whilst it is permanently connected to the trickle charger which is then permanently connected to the mains?

  • \$\begingroup\$ I don't see why not. Note the voltage may vary quite a bit. \$\endgroup\$ Jun 14, 2016 at 1:30
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    \$\begingroup\$ Well, now I've built something like this, and it does work. The only problem is that if the charger is smart, it may think something is going wrong and show an error code and stop charging. If the charger is dumb, it should work fine. \$\endgroup\$ Jan 8 at 18:50

1 Answer 1


Not sure how well the trickle charger would deal with a varying load. Also, not sure that the trickle charger is protected from being back driven by the battery, or possibly draining it. These are things which you should investigate. Some well placed diodes here could really help.

For any sort of important application, I would recommend purchasing a dedicated UPS. There is quite a bit that goes into their design.

  • \$\begingroup\$ Thing is 12V UPSs are very expensive as they're typically only used in industry. Might be £100+ for a nice DIN rail mounted one in green. \$\endgroup\$
    – Paul Uszak
    Jun 18, 2016 at 1:57

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