Here's an eBay listing for a 250 mAh version:
https://tinyurl.com/y5ghywyh
As for field charging, you get MORE FUN per hour by having several batteries, charge them all up the night before. It takes 20- minutes to an hour or more to recharge depending on the charger, so field charging is not very practical, unless you pay to get a multi-charger that can charge 4 or 5 at a time (I have really good one that is very adjustable, by HiTec but it's pricey. Chinese knockoffs cost about $45-50). Like this:
https://www.ebay.com/itm/HTRC-X4-Mi...975377?hash=item340b7c0091:g:CygAAOSwpI9bdaNL
Oddly, I can't find the original HiTec version of this listed (might be discontinued,I got mine 5-6 years ago). That type is nice in that the charge rate can be adjusted (HiTec's 100 mAh to 500 mAh IIRC), and displays the voltage and charge rate on an LED digital display for each battery. Also it can be powered both by 120V AC as well as 12V DC.
Here's a basic one at a very good price, $11.99. Not adjustable, no display, just an LED light for each cell being charged (this kind of charger usually shows a red LED when charging and green when charged, and stops charging, but this one may not be that way. Some light up red when charging and STOP being lit up when charge is done, saves power on the source battery but can be aggravating). USB powered. For field charging you can use a Battery Bank as shown in the photo. But still charge them all up beforehand, and only field charge if you want to make more flights than you have pre-charged batteries for.
https://www.ebay.com/itm/5-Port-Par...488687?hash=item41f02f096f:g:c9EAAOSwLXNbvQ8q
