I emailed Sony and they said that they only recommended the NP-FP30."We can neither recommend or endorse any third-party products. To use any other products may cause unforeseen complications or damage and could negatively affect the product's performance. Damage caused by the use of any third-party products is not covered under your warranty." But Sony lists the NP-FP50, NP-FP-70, and NP-FP90 on their battery chart as compatible with the HC21 - this chart doesn't even list the NP-FP30. I have a question emailed to Sony regarding this...as who knows what to buy?

I'm having the same problem - I bought a bargain-priced battery - thought it was the company - sent it back after repeatedly getting the "use infolithium battery pack" message. Bought a battery, from a brand name (but not Sony) that uses a bunny (to go on and on) which states the Sony HC21 as compatible - I still get the message and error code (C:04:00). I'm very frustrated with this. (Plus, the company I sent the original battery back to, put it in their same-model Sony and it works fine) What's up here? Anyone have a solution? I'm concerned now that even if I buy a "Sony" battery - will that even work. I'm a few weeks away from a trip of a lifetime. HELP!