I am trying to calculate the maximum charge rate of my AGM powersafe batteries 12 V 170 Ah, the data sheet says it's "0.5c¹⁰ amps"

I think 0.5 C makes 85 A, but not sure about the 10 to the power of. What does that mean?

Any suggestions? Thank you

Link to the data sheet:



figure 4

  • \$\begingroup\$ When I put it through an expondant calculator, comes out at 1.96amps, which I find very hard to believe, at that rate it would take almost 100 hours to charge \$\endgroup\$ May 29, 2023 at 10:27
  • \$\begingroup\$ 0.5 C of 170 Ah is 85 A, not 85 Ah. \$\endgroup\$
    – winny
    May 29, 2023 at 10:34
  • 1
    \$\begingroup\$ It does not mean raising to a power of 10. It's not a superscript, it's a subscript. \$\endgroup\$
    – Justme
    May 29, 2023 at 10:36
  • \$\begingroup\$ @winny yes sorry good to be specific.. \$\endgroup\$ May 29, 2023 at 10:37
  • \$\begingroup\$ @justme what does it mean then please? \$\endgroup\$ May 29, 2023 at 10:40

1 Answer 1


It's not not 0.5C10, it's 0.5C10, ie. 0.5 times the C/10 charge rate, or (theoretically) 20 hours for 0% to 100% charge.

For a 170 Ah battery that would be 0.5 x 170/10 = 8.5 amps.

  • \$\begingroup\$ Thank you very much, I'm surprised it's as low as 8.5 amps , that's exceptional slow for a VRLA AGM battery , they are normally around 0.3c , would be 51 amps \$\endgroup\$ May 29, 2023 at 11:48
  • \$\begingroup\$ manuals.plus/enersys/… Graphs in this manual (figure 4) seem to suggest charging from 10% to 80% in 6 hours \$\endgroup\$ May 29, 2023 at 11:51
  • 1
    \$\begingroup\$ I would have thought that c_10 was the capacity when rated at the 10 hour rate, so 170 for the OP's battery. However, that assumption doesn't square with the presented time to recharge graph any better than your assumption, so I'm puzzled. \$\endgroup\$
    – Neil_UK
    May 29, 2023 at 13:18
  • \$\begingroup\$ 10% to 80% is 70%, which should take 7 hours at C/10 or 14 hours at 0.5C/10. There must be something they aren't telling us (higher current during bulk stage?). Anyway the maximum charge rate is stated as 'unlimited' so you should able to safely go up to C/10 or even higher (eg. C/5) until reaching peak voltage. \$\endgroup\$ May 29, 2023 at 13:32
  • \$\begingroup\$ I know AGM batteries can take almost unlimited currently for the lower part of the battery, they current only has to be limited for the top chunk (technical term) \$\endgroup\$ May 29, 2023 at 15:43

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