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So I had a sealed lead acid battery which have a characteristics of 4Ah and 6v and 20h.

First if all when I searched about discharge rate of this kind of battery I found this "The sealed lead-acid battery is rated at a 5-hour (0.2) and 20-hour (0.05C) discharge".

I incidentally had a lipo battery of 7.2v 1000mAh rated at 35C which after a bit of research , it turned out that this number is the maximum safe current it can deliver so 35 * 1000 which is 35000mA or 35A.

So is this the same for lead acid battery? So for my battery I get 0.05*4000 200mA only or I mixed two different meanings together ?

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  • \$\begingroup\$ you cannot determine the discharge current without knowing the load resistance \$\endgroup\$ – jsotola Nov 7 '19 at 16:38
  • \$\begingroup\$ @jsotola thanks for your note I meant the maximum safe discharge current \$\endgroup\$ – Shams M.Monem Nov 7 '19 at 16:41
  • \$\begingroup\$ If you have a part number you can normally check the datasheet. It should have a Max discharge current and time you can run at that max current. \$\endgroup\$ – Robert Fay Nov 7 '19 at 16:46
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    \$\begingroup\$ You use the data sheet for the battery. \$\endgroup\$ – Andy aka Nov 7 '19 at 17:10
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    \$\begingroup\$ If you have reason to suspect that it's similar to other, better-documented batteries on the market, you look at several datasheets of hopefully-similar batteries. If there's not much spread in the parameters, you cross your fingers, hold your breath, and make a guess. Not having good data on a battery is a good reason to not design it in, unless you really need to save money. \$\endgroup\$ – TimWescott Nov 7 '19 at 17:18
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Many batteries will give you a chart in the datasheet. This is the one for a similar rated battery from Panasonic BP4-6 The Time is dependent on the current out. enter image description here

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  • \$\begingroup\$ So this image seems promising, but I don't know what will be the characteristics when there is a battery that have many cells like my 6v 4ah \$\endgroup\$ – Shams M.Monem Nov 7 '19 at 16:55
  • \$\begingroup\$ Most are going to have several cells. The one in the datasheet has 4 cells hence the V/cell rating. \$\endgroup\$ – Robert Fay Nov 7 '19 at 18:06
  • \$\begingroup\$ Unfortunately this table doesn't say anything about the maximum discharge current, except that 60C (the 5 minute discharge) seems to be within that maximum. \$\endgroup\$ – Elliot Alderson Nov 7 '19 at 20:52
  • \$\begingroup\$ In the data sheet though it gives Max. Discharge Current 60A (5sec) for this specific battey. \$\endgroup\$ – Robert Fay Nov 7 '19 at 23:48
  • \$\begingroup\$ @ShamsEl-Deen The characteristics of different brand SLA batteries of the same type and size are usually similar, so this chart will probably be close enough. \$\endgroup\$ – Bruce Abbott Nov 8 '19 at 4:23
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If all of the information you have about the exact battery you own is the statement about how the battery is rated, then you should assume that the 5-hour rate is the maximum rate. That's 0.2C or 800mA. Note that the actual capacity of the battery may be significantly less than 4Ah when the discharge rate is 0.2C.

The "6v4ah/20hr" marking is not a part number so it doesn't help us to find the manufacturer's datasheet for the exact battery you have.

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