I’ve been out of the R/C hobby for 25 yrs, but my young boys found my old truck. Threw away all the old battery packs, bought a new NiMH 3000mAH 7.2v battery. I have an old Hobbico 905 charger, can anyone tell me how long to charge this battery? Or will this even work with a 25 yr old setup?

I wouldn't attempt it. You really should be using a peak detection charger.

Charging Instructions:

Do the math.... an empty battery will take about 50 minutes. Bu I agree, get something decent, a simple B6AC charger can be found for about 40 bucks.

While I agree it's best to use a peak detection charger, you can do the same by periodically touching the battery every couple of minutes until it starts to get warm, then you know it's fully charged. Measure the time it takes and then you know for next time you charge it. This is how we charged packs back in the day... it's not fool proof but will certainly gitterdone.

And then when you get distracted, they explode. It's a very dangerous method.

Thanks for the replies.

Yup, back in 1984 my neighbor built a gold pan RC10 and the only way he charged it was with mini jumper cables to connect to the 12V battery of his dad's 1:1 automobile. There was no form of shutoff, anyway his mom called him in for dinner and he left the battery on the charger for about a half hour and came back to a crispy burnt up pack and charred remains of cables with burn marks all over the engine compartment of his dads car. Back then our NiCd packs were only 600mAh and they would typically charge in about 5-10 min max. I think the Hobbico 905 has a 15 min timer and may take several cycles to fully charge at 3000mAh, probably a very low risk of causing fire, especially at only 5A.

Quick math 3000 mAh = 3Ah / 5A = 0.6 Hours, so somewhere around 36 min for a fully discharged 3Ah battery at 5A

You can always get from Amazon, Aliexpress etc a cheap temperature alarm module. Even a cheap temperature controller like a W1209 can be used a a simple programable temperature sensor/alarm