Multimeter battery voltages

[DRo]

Hi, I'm new to this and have been looking at using my multimeter to check battery voltages. Now I've found plenty of info and videos of people explaining what voltages should look like for fully charged batteries of different types, but I've not really found anything showing what the numbers look like at various levels of discharge. Is there a datasheet or chart that anyone knows of that would tell me roughly what percentage of charge my battery is at, for different types of batteries? eg. So I can say, I have a 6 cell nimh which is 7.2v (6 x 1.2v) and it's reading X.Xv on my multimeter, so that means it's about Y% charged. And also so I can see at what voltage various battery types are considered dead. I guess mainly nimh and lipo, but even things like AAs, more out of interest than anything.

 

If anyone could point me to any info, I'd appreciate it, as at the mo I can see my battery voltage, but I don't really know anything useful to do with that information!

 

Cheers

[BigGinge]

That’s quite a complicated question. 
 

Each battery pack design (even for different types of pack with the same underlying chemistry type) will have its own characteristic discharge curve which will be highly dependent on a number of factors such as the battery temperature and discharge rate. So to get a single figure for the % capacity used requires a lot of knowledge about your pack and how you will be using it. 
 

The page linked below goes into a little detail about this. 
 

http://learningrc.com/lipo-battery/

[DRo]

Ah thanks - that looks really interesting. Will give it a good read later on. I might have guessed there wouldn't be a simple answer! 😄

[mrhavana]

The nominal voltage for most NiMH cell is 1.2v so a 6 cell pack will have a nominal voltage of 7.2v. This will charge up to around  8.35 - 8.4v and should not be discharged below about 6v. 

 

Alkaline type batteries typically have a nominal voltage of 1.5v, fully charged are about 1.65v and are considered depleted around 1.0-1.1v.

 

Lipo batteries have a nominal voltage of 3.7v, maximum of 4.2v (HV lipos up to 4.35v), and minimum of 3.3v. The lower limit is technically 3.0v, but as the chemistry of the lipo is damaged below 3.0v it's safer to use 3.3v - 3.5v as a lower limit. The other thing is that there is very little capacity stored below 3.6v. The table below is pretty old, but is unlikely to have changed significantly over the years.

 

Lipos are best kept at a storage voltage of 3.8v .

 

 

For lipos you might want to consider a cheap voltage meter. The percentage algorithm is a bit off on mine, but the voltage readings are accurate when tested against a calibrated mulitmeter. It's really useful for comparing individual cell voltages in a multi-cell pack and will even show you the highest and lowest cell voltages and the variance between them. This can be particularly useful in identifying a faulty or dying cell. 

 

 

 

[DRo]

That's great info - thanks!