Maybe I missed some replies but looks like nobody proposed this so far so...
TDS210 is cute, would be a shame to replace it with god knows what portable chinese or old overpriced Fluke wasting money.
TDS210 is small, light, portable with its nice handle, and probably draws bugger all power.
So why not simply buy no scope at all, and just make that lovely TDS210 portable ?
With a smallish size battery and cheap small dirty chinese inverter, should do it ! Just stick the pack to the TDS butt whenever you need to take it outside and/or want it floating, and that's it !
Better yet : don't know the internals of the TDS210 but being low end and cheap and small... with some luck the internal SMPS supply puts out a single output voltage and might not even require a standby/power-on signal line. Might be just 12V ? Or whatever.
So just do away with the inverter and just connect a battery or battery pack of the required voltage to the scope. Solder two wires to the SMPS inside, a couple beefy low drop diodes to avoid frying anything, then add a little connector to the back of the case of the scope, or if you don't like to mutilate it, there must be some cooling grills I presume (no fan IIRC) through which you could route your two wires.
Would work out much cheaper, and you would get to use your cool TDS210 all the time.
I would at least investigate the possibility, were I in your shoes !
Hoping to be in your shoes one day, but prices for a TDS200 series over here are insane, people smoke funny stuff it seems.
Plus I would like a 220 or 224 which is rare, and with the "communications/interface" optional module at the back, rare too. I saw such a module for sale standalone recently over here, for 50 Euros. Asked the seller about it.... been a month, still no reply, still online though ! According to the messaging system, guy still has not even READ / seen my message.... hoping nothing bad happened to him, I want his module !
https://www.leboncoin.fr/equipements_industriels/1987919695.htm