Rechargeable 9V Batteries - High-Performance Lithium-ion Battery 4 Pack with 4-Bay Speed Charger - Leak-Proof Ultra Long-Lasting 8.7 Volt 1300x Cycle Times with a 10-Year Shelf Life

I purchased these for my wife to use in her "Tens" unit. The tens unit came with nickel metal hydride batteries (NiMH or Ni–MH), and she was constantly recharging two batteries a day to keep the unit going. After I installed one of these Li-on batteries in the device it allowed my wife to use the tens unit, (during the day), for two days straight, and it still had power remaining. I am very "picky" about Lithium-Ion batteries, and these were a quality build.***UPDATE***I cannot recommend this set, because it does not offer a transformer or power source, and additionally has no way to discharge and recharge the batteries properly. I found two of the four batteries to only supply 2.4 volts and a little over 7 volts on the second one. They should charge to approximately 8.4 volts DC which in our situation was required to properly operate my wife's "Tens" unit. It is standard for a 9 volt Lithium-ion battery to charge to approximately 8.4 volts, and not the 9 volts as stated, but it should provide the needed voltage, and current for a lot longer than a regular, alkaline, or Ni-Mh battery. Too many of these battery/charger sets offered, want you to plug their charger into a laptop USB port or provide your own USB charger, which may not provide the needed current to each channel of the 4 charger ports. If they want their product to operate properly, the manufacturer should provide the proper charger with these units. Especially at the price of this packaged product .

Work really well and charge really fast. Excellent quality!!

Much longer lasting than I expecting. Using in my TENS unit and they last for weeks for an hour usage per day. Outstanding.

I thought I might try some rechargeable 9V lithium batteries for my Fishman ToneDEQ guitar pre-amp (which consumes batteries faster than I like). I settled on the “ccvv” brand after reviewing other options due to the 850mA capacity, higher terminal voltage, and the internal control chips. I received the four 9V batteries and charger, and being a retired Electrical & Quality engineer, I wanted to track their performance. I’m glad I did as one appears to be slightly different from the others.I numbered the batteries [B1, B2, B3, B4] and measured their initial Open Circuit Voltage (OCV). [7.87, 7.83, 7.76, 7.81 respectively]. I then loaded them into the charging base keeping sequential positions [I called these C1, C2, C3, C4], and connected the base to a 5V / 2A USB charger.After about 4 hours all the red LED’s had turned green so I removed the batteries and re-measured them [8.57, 8.6, 8.66, 8.26 respectively]. Observing B4 measured 8.26 while all the others measured about 8.6, I wondered if there was something different about this battery. I returned B4 (only B4) to the charging base in position C4 for another 2.5 Hrs. At the end of that time, it still only measured 8.27V, so it was obvious it would not reach 8.6V like the others. I should note that none of them seemed warm from charging.I let them all sit overnight and re-measured them for any noticeable self-degradation… there was none [measured 8.57, 8.59, 8.64, 8.26 respectively]. At this point, I returned B4 to the charger in position C3 to see if the charging position had anything to do with the voltage difference on B4. The LED was red for less than a min, then turned green. After sitting 6 Hr in the C3 position, B4 measured 8.28V, so it appears the charger position had nothing to do with the voltage difference, and there is something internally different about B4.My Fishman ToneDEQ is a bit sensitive to voltage, so I’ll need to see if it is happy with the B4 lower voltage or not. The other three should work fine, but I would have preferred them all to be similar. I may need to return these if B4 is a problem.

Holds charge well in storage. Lasts long in use.

This company went above and beyond. Replacement of charger, and so quick to respond.I’ll be suggesting this company to my friends. Batteries are top quality.Thanks so much….this type of customer service is rare.

Works good, but not exactly 9v.

As advertised by seller