Sphero BB-8 with new batteries won’t charge.

Replacing rechargeable lithium batteries should be a no-brainer as long as the replacement is either the recommended or compatible one. Like all rechargeable batteries, replacements must meet the same specs. Consumer products with manuals describe general operating principles along with guidelines on charging. This includes tell tale indicators. Review the manual for guidelines on what to look for unless you remembered how the indicators let you know of charging conditions . They’re the only clues of what the charging system is doing. If the charging indicator doesn’t turn on, there may be a failure in either the charging circuit, corroded/loose connections or battery.

Rechargeable nickle cadmium, nickel metal hydride and lithium batteries have unique charging circuits to ensure against overcharging.