I think it will be relative, but the 70 battles a day are at least missundertanding, in my opinion just false:
You can play this 70 battles only when you start at 100% ECR but afterwards the ECR won't refresh back to 100% in one day. So if you play everyday you can play a absolute maximum of 48 battles and if you play only once a day than even only approximately 40 battles.
It is not so, that we cannot discuss if this is enough or not but they shouldn't publish information who are at least missunderstanding.
Just look:
If you are at 50% ECR and start a battle you will be afterward by 49.5%.
To avoid increased ECR-Loose you need now to take a brake for 30 minutes.
After 30 minutes you can play the next battle, so we go back to 1.
Cause you can do this only every 30 minutes you can play a maximum of 2 battles a hour what means 48 battles a day.
BUT: No human can do this or will do this, a human want to sleep and not wake up every 30 minutes to play a battle, so if you play once a day all battles you will use more ECR but ECR-regeneration will be the same, so you can play less battles. In this case you can play only 39, maybe 40 battles a day to avoid moving under 50% and not 70 like the splinterlands-team mentioned.