At those voltages you are lucky not to have had a fire. I'm actually inclined to suspect the voltmeter as I would have expected flames by 4.5V
Probably those batts are bad built or has "impurezas" inside the chemistry.
Bad, bad, very bad. Check voltages again with another multimeter, if they continues being >4,3 volt recycle them
Need some help. I'm going to buy a XPE and XPG leds and install them into these 2 flash lights. The last Mod I did was installing a Q5 into a light that had a luxeon led. When done it only ran for 10 minutes on a fully charged battery but was very bright.
What do I need to considered before installing the led. Example VF voltage? Amp? Driver?
I think the driver in this light was meant for a cree Q5 but both of the light I bought have generic leds in them.
I may use the existing driver. Any advice would be useful.
Vf is not usually something that you usually get a choice in, you get what you get. You can buy them sorted by forward voltage but it is going to treble the price at least.
An XP-G does prefer a lot of current which the driver probably won't be able to provide - but it should be brighter at a given current than what you are replacing. Definitely worth a try. Heat should be less of an issue with a more efficient LED.
I saw somewhere advertising XP-E R5s recently but this may have been a typo (or lying) - I've not seen anyone offering the XP-E R3 despite its allegedly having been available all year.