The voltage read out from this Li-on battery meter (an affiliate link, it matters to someone people apparently) is about 5.99v at 99%, which is different from 7.4v listed on the battery. The battery meter comes with very little instruction.
Also, I thought this is a 2-cell battery. But the meter can only reads it as 1-cell. For those who are familiar with the meter and RC Li-on battery, please explains the discrepancy? Thanks in advance.
Cyberbrick battery specs
You should probably disclose that you’re using an affiliate link.
I’m pretty sure this style of LiPo tester expects a 2S LiPo to use a 3 pin connector, with the middle pin connected to the contact between the two cells.
This is how the tester can measure each individual cell, but the CyberBrick batteries probably have an internal management chip that handles the balancing, making the requirements for a charger less elaborate.
5.99 and 99% sort of looks like a max value somewhere in the code of the tester and I have a feeling that the voltage across the terminals of the battery might actually be a little higher.
If you decide to take the pins out of the connector or use test leads to connect + and - with an extra pin in between, be aware that a LiPo/Li-ion battery like this can supply quite a bit of current and will probably melt stuff if shorted, so be careful 
The panel on the Meter shows it’s using a 1S configuration which is incorrect, the battery is a 2S configuration. Your readout is probably saturated. Read the manual and see how to set 2S configuration.
A couple of problems here…
You do not have the connector installed correctly.
I don’t know what “ve” is supposed to be, and I’m too lazy to go look it up (I probably have one of these meters in my box of older radio control related gear). But the black wire on the connector should be aligned with the “-” pin and the red with the “1” pin.
I’m surprised it is reading anything at all. I suspect it may not be reading correctly.
These pins on the battery checker are really intended for a LiPo pack that has a “balance tap” that allows the checker to see the individual cells in the pack. You would actually see two voltages if this pack had a balance tap, one for each of the two cells.
It says 1S Li-Ion but also 99% which is wrong. I think it’s confused. A Li-Ion cell should have a max voltage of 4.1V.
If the plug will fit, try the NiCd input. That’s designed for packs that don’t have balance taps, and odds are it’ll read the pack voltage correctly. Ignore anything it says about %.
Although, it may in fact be reading the voltage correctly. In which case you should charge the pack. The minimum voltage for a LiPo is 3.0V/cell, so 6.0V for the pack. You’re at the minimum.
I’d add that, IMO, on first blush it looks kind of bad that BBL is selling what appears (based on the 7.4V rating and 8.4V charge voltage) to be a 2 cell LiPo battery that doesn’t have a balance tap. Balance taps also connect to LiPo chargers that ensure individual cells never exceed their absolute maximum voltage (4.2V), because doing so can cause them to catch fire. “Unbalanced” LiPo pack charging is a no-no.
But it would arguably be criminally negligent to sell a LiPo that is unprotected and so, could be overcharged. I suspect this pack has “button top” cylindrical LiPo cells (or the pack has something called a Battery Management System, a small circuit that protects otherwise unprotected cells). This type of built-in protection circuit prevents cells from being over-charged or over-discharged (which is a fire risk). And also allows them to be safely charged as a single 8.4V battery with no balance tap.
I suspect built in BMS as it simplifies things and takes care of most risks that could cause harm to novice users. Also looks like “charger” they are selling is outputting only 7.4V so this battery will never be at full capacity.
Edit:
I have ordered few of those as have different use for them and might sacrifice one for the science.
