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I have a thermostat (Siemens REV200) which runs on 2 AA batteries. I've put in 2 brand new (A brand) batteries but the device keeps showing me low battery power signals. How do electronics usually measure battery life?

I was thinking of connecting a power supply to it which exceeds 3 volts or 2 amp. Would this be a solution?

Mehdi Nellen
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  • Check out an example AA battery datasheet: http://ww2.duracell.com/media/en-US/pdf/gtcl/Product_Data_Sheet/NA_DATASHEETS/MN1500_US_CT.pdf Under "Constant Current", you can see how the battery voltage drops over time at different loads. Typically the device will measure the battery voltage and convert (using a rough approximation) to a percentage. – jpwr Feb 18 '16 at 14:47
  • In many devices it's a simple voltage measurement, which can be fooled if the battery chemistry isn't what the designer expected. –  Feb 18 '16 at 14:47
  • Maybe the battery contacts are corroded, clean them up using a pencil eraser. – Bimpelrekkie Feb 18 '16 at 14:49
  • @FakeMoustache I already tried with contact spray, but the device is brand new and the contacts were clean already. Also the voltage of the batteries seemed normal. – Mehdi Nellen Feb 18 '16 at 15:22
  • Then I think this thermostat is broken, send it back to Siemens ! – Bimpelrekkie Feb 18 '16 at 15:27
  • It hasn't got any warranty left, I got the device from a friend who bought it but never installed it. I will try to give it a couple of tenths of volts to see if anything changes. Thanks for the help! – Mehdi Nellen Feb 18 '16 at 15:47
  • Possible duplicate of How to calculate battery life – Scott Seidman Feb 18 '16 at 16:29

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Typically low battery (for primary- aka non-rechargeable) batteries or cells is indicated when the voltage (preferably under load) drops below a set threshold.

Replacing primary alkaline cells with a different type such as NiMH rechargeable cells can result in a 'low battery' indication because the cell chemistry is quite different, resulting in a lower voltage- 1.2V vs. 1.5V in that particular case- even for freshly charged batteries.

We have no way of knowing whether attaching an external power supply could cause any damage- if the thermostat has problems replacing it or repairing it would probably be a better course of action.

Spehro Pefhany
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  • The device is brand new, and the alkine batteries as well (Duracel), I've measured the voltage and it slightly exceeds 1.5v. Too bad I can not provide you with any circuitry information (it is not provided by Siemens) – Mehdi Nellen Feb 18 '16 at 15:19
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    Any chance it got wet or leaking batteries corroded or left residue on the PCB? – Spehro Pefhany Feb 18 '16 at 15:22
  • no, contacts seem to have no resistance till the first components on the pcb. Quite enigmatic, thanks for your suggestions any way. – Mehdi Nellen Feb 18 '16 at 15:42