I have a couple of lead acid batteries that need to be stored so I though up of a simple trickle charger with the following objectives in mind:


  • Should waste least amount of power so that power could be applied to the batteries as long as possible
  • Should be simple as it will be operated manually (voltage will be checked with a multimeter and connected and disconnected manually)




  • AC-DC power module from Hi-Link (part#:HLK-20M15) which outputs 15V with a max of 1.33A (20W) which has output short circuit and over current protection and self-recovery.
  • The diode for reverse polarity protection as well as a drop 1.1V which will allow the max output voltage to be 13.9V and
  • The 1ohm resistor is added as a current limiting resistor which can drop 1.33V at max output current.

Reasoning: A total voltage drop of 2.4V (diode + resistor) from a 15V supply should allow me to charge the battery from 12.6V. I will be using a proper tested and certified charger for bulk charging if the voltage drops below 12.6V.

Question: All that said I wanted to know if:

  • This should suffice from a safety point of view or any changes are required
  • Does charging to 13.9V for storage good enough for long term storage since I won't be drawing any current from it because I've seen some batteries require boost voltages of about 14.4-14.6V and some people suggested boost upto 16V.
  • \$\begingroup\$ At a minimum NEVER let a battery remain below 12.6V (maybe 12.8V) for any longer than necessary. That is the sulphation limit. Manufacturers usually specify float voltages for standby mode (which you want)(about 13.5V) and deep discharge/power mode (slightly higher). As ever battery university is a good resource. \$\endgroup\$
    – Russell McMahon
    Apr 24, 2021 at 12:19
  • \$\begingroup\$ Thanks for the battery university link, it's a gold mine!. \$\endgroup\$
    – Canute S
    Apr 25, 2021 at 5:43

1 Answer 1


The simplest way to not waste power is to lower the voltage you start with to just about the "float voltage" of the lead acid battery. If you can get an adjustable switcher, that would be a good place to start. At the float voltage a LA will take forever and a day to charge back up so you want to raise the voltage when the battery has been discharged. This is usually about up to 15V.


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