I'm not an electrical engineer, but I do have a question regarding voltage and timing.

Approximately how long will it take for 171v to drop to 100v with a 75w light bulb?

Im only looking to figure out how long it would take to discharge a battery.

The battery I am discharging is a 2005 Honda Accord Hybrid IMA 144V Nickel-Metal Hydride battery.

6.0 Ah

  • 5
    \$\begingroup\$ Similar question: approximately how far can you get on a full tank with a car which has a top speed of 144 km/h that uses 75 liters per km? \$\endgroup\$ Mar 10, 2018 at 20:09
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    \$\begingroup\$ The similarity here is that there's no datasheet, no information about the size of the fuel tank, Ah (Ampere hours) in your case. It's one parameter that is missing that is needed to solve this simple puzzle. \$\endgroup\$ Mar 10, 2018 at 20:14
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    \$\begingroup\$ This question is not very hard to answer, but just like other bad questions, it indicates some very bad design. \$\endgroup\$ Mar 10, 2018 at 20:24
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    \$\begingroup\$ you indicated that you have the battery. ... get a stopwatch, a voltmeter and a 75W lightbulb and do the experiment yourself ... why are you even asking your question? \$\endgroup\$
    – jsotola
    Mar 10, 2018 at 20:27
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    \$\begingroup\$ Use a DMM ammeter and count Ah \$\endgroup\$ Mar 10, 2018 at 20:57

1 Answer 1


Using your figures: 171 Volts and 75 Watts means 75/171 = 0.4436 Amps.
6 AH / 0.4436A = ~13.7 Hours. Your battery will not slowly go from 171 Volts to 100 Volts. It will stay close to 171 Volts and when it gets empty drop rapidly.

You state "144V Nickel-Metal Hydride battery." so I don't understand where your 171 Volts comes from.

  • \$\begingroup\$ Honda used 1.5V D-sized cells in their hybrid systems. Making some assumptions based on the OP's numbers, there's 96 cells total, which makes 144V. But when fully charged, the cells are probably around 1.78V, which makes 171V. \$\endgroup\$
    – Dan Laks
    Mar 10, 2018 at 20:37
  • \$\begingroup\$ The current voltage is 171. 144 is the ideal operating range. But thank you very much for answering my question. \$\endgroup\$
    – rcpayung
    Mar 10, 2018 at 20:38
  • \$\begingroup\$ It not the ideal range. it is the max no load charged voltage If you are trying to estimate Ah capacity this is a very inaccurate way to do it. A 75W bulb will only be 75W at the rated voltage , not 171V or 144V or 100V \$\endgroup\$ Mar 10, 2018 at 21:07
  • \$\begingroup\$ @DanLaks such high cell voltages seem unusual for the Nickel metal-hydride cells which are usually nominally 1.2V and exhibit about 1.25V per cell when fully charged. \$\endgroup\$ Mar 10, 2018 at 22:03
  • \$\begingroup\$ @Jasen, hm, you're right. I wasn't considering they were NiMH cells. So I guess there's 120 cells in the pack (or more if there's multiple strings in parallel). 171V does seem high then. EDIT: I'm finding a couple sources online that say some NiMH cells are fully charged around 1.4V, so maybe 171V is about right for 120 cells. \$\endgroup\$
    – Dan Laks
    Mar 10, 2018 at 22:07

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