How to Solve Low Battery Back Up Problem in Inverter


My Exide 150 ah battery gives power back up for two hours, but the seller promised that the battery would give backup for at least 4 hours, Is my battery failing?


Not exactly, first of all you should know some facts about ‘Discharge Rating’ of Lead acid battery. You may have noticed something like ‘150ah @ C 20’ on your battery. Have you ever asked about this so called ‘Discharge Rating’ (not AH rating) to your battery dealer?

99.99 % buyers don’t know anything about the Discharge Rating of their battery.

Normally most lead acid batteries used for Home Inverter purpose are ‘Rated @ C 20’.

battery discharge rate


Let me explain in simple words

If you have 150 ah battery with 20 hour discharge rate, then you should use only one fan (75 watts) and one CFL (20 watts)to enjoy extended battery backup.

If you draw more than 95 watts from a 150 ah battery, then your backup time will be reduced significantly. You will be left with very low backup if you use four ceiling fans and 3 CFL’s simultaneously with 150 ah battery.

Most people think that, if a single fan runs for 16 hours with fully charged 150 ah battery, then we can expect a 8 hours backup for two ceiling fans with 150 ah battery. This is a totally wrong idea.

Actually, if you run two ceiling fans (75+75=150watts) simultaneously with 150 ah battery, you were drawing more than 95 watts, So clearly the backup time will be reduced and you can expect only 5 to 6 hours backup.

Remember that if you run only one ceiling fan (75 watts) with 150 ah battery, the expected backup time will be 15 to 16 hours. Now it’s clearly evident that ‘More you use, more you lose’

Concurrent Usage limit for Optimum Battery Backup of Home Inverter batteries (@C20 discharge rate)

80 ah – 48 watts

88 ah – 53 watts

100 ah – 60 watts

115 ah – 69 watts

135 ah – 81 watts

150 ah – 90 watts

165 ah – 99 watts

175 ah – 105 watts

200 ah – 120 watts

Power consumption chart of normal Home appliances

Ceiling fan – 75 to 85 watts

Tube light – 40 watts

CFL lamp – 15 to 25 watts

Mixie – 400 to 550 watts

Laptop – 65 watts

Desktop PC with 19 inch LCD monitor – 200 watts

21 inch Normal TV – 100 watts

14 inch normal TV – 70 watts

32 inch LCD TV – 85 watts

32 Inch LED TV – 55 watts

  • Nivin

    I have Luminous ILTT 18048 150Ah battery. My maximum load is only 50 Watts(all LED bulbs 9+9+12+12+8W). But I am getting only a maximum backup of 9 hours with this 50W load.

  • Thank you for beautifully explaining the battery load and about battery discharge