EBL Rechargeable 9V Lithium Batteries 5400mWh Test Review And Unboxing, I take a look at these USB rechargeable 9 volt batteries made for small electronic devices like radios, smoke detectors, walkie-talkie, alarms clocks, microphones and so on. These lithium-ion batteries have an excellent low self-discharge rate. This makes them best suited for slow discharge devices like Smoke detectors. EBL claims they supports over-charged, over-discharged, over-voltage, and short circuit protection. All of these function will help the batteries to last much longer than alkaline cells.

You can find these EBL batteries here at a fair price. https://amzn.to/48TZn1Q