A Cycler is good but you can manage with just a Walwart, a suitable car bulb and a voltmeter/ammeter.

Charge the battery fully.

Leave for 2-3 days.

Find a 12 volt bulb or other load to give a drain about equal to the capacity eg 600 mah should be loaded to 600 ma. approx.

Check the voltage after 40 mins and every 5 mins after that. Stop at 1.05 volts per cell. Work out what capacity you have. [Current in ma times minutes divided by 60]

Anything less than 75% should be binned.

I started doing this when the club I was with had a bunch of packs fail early in the season. I had some fairly small capaity nimh packs that i used in small models and found that they did 3 seasons reliably then it was a downhill slide.

I did buy a fancy charger/cycler eventually