So i bought some of those all-in-one 18650 battery shields from a well known Chinese place. When I plug the battery in it seems to charge but the 5v and 3v pins have zero volts.
When I remove the battery and place it in a torch, it works fine. Plenty of power, but take it out of the torch and place a multimeter on each end it shows 0v.
is this because it's got a built in protection board? Do I need to get an unprotected battery because the battery shield also has one built in?
Who knows ?
You might get a better answer if you provide links to the boards you are referring to, the forum cannot know unless you tell us.
Not many of us have crystal balls in working order .....................................
is this because it's got a built in protection board
From what you have said I would say no. I think your DVM is broken. Have you done any tests to check it is working?
If by DVM you mean the battery shield, I bought 4 of them and they all have the same issue.
What I can't understand that the multimeter is showing 0v on the battery when the battery is not in the shield, but put the battery in a torch and it works fine.
No, he's talking about your multimeter. It sounds like it isn't working. If so, you may have blown the fuse trying to test current. There should be an access panel to the multimeter batteries and fuse on the back somewhere. Another possibility might be a broken lead or connection. But my money is on the fuse. If the charged battery works, your meter will show 4+ volts if it's working properly.
But my money is on the fuse.
In all the DVMs I have seen the fuse only protects current readings so it would not affect a voltage reading. However it might affect the voltage reading if the DVM ( Digital Volt Meter ) has only two sockets in it. Most have different sockets for volt and current measurements with a common ground.
If by DVM you mean the battery shield,
Basically what you described is impossible, so we have to find out what you are not understanding.
You are quite correct - dodgy lead on the meter. Swapped it out and now the battery reads as expected. oops.
These battery shields are a bit odd in that if you insert the battery, it looks like it's dead. You have to then plug it into charging power for a short time. After that the outputs are live.
Thanks for the help