It's a good idea to clean dirty battery contacts with a cotton swab and alcohol. It helps maintain a good connection between the battery and the power tools.

Please fully charge before first using / At least charge 1 time every 3 months / Remove the battery from the device when not in use to prevent slow discharge.

Tricks to improve Makita BL1820 electric tools battery life and performance

When using cordless tool batteries, it pays to plan ahead.

Keep your battery properly charged and you can expect a long life.

Most short runtime issues occur due to battery neglect, not failure.

If you use your Makita cordless tool infrequently, be sure to charge the battery when you feel a slight decrease in power.

Draining the battery down to the point where it no longer runs can damage the battery. Periodically charge the battery overnight to achieve optimum runtime and lifespan.

If you use your Makita power tool on a regular basis, we would also recommend a second battery to keep your project moving while you are charging the first one.

for more details please check

https://www.aussiebatt.com/makita_BL1820_tool-battery.html