I've got an Ultimate that came from Lidl years ago, about £6 then 🤣 My favourite! Has a dual charge 6 and 12 which is great for me. A slow charger , but to 100% and reliable. I'd recommend one over a lot of Flashy , expensive chargers. As for battery parrell charging, depends on the battery some you win some you don't , but worth the try. AA chargers ,any battery only has a certain capacity, I've never quite understood how a couple of AA's will replace a massive great Lead /Acid. Leving aside Oddessey or Optima batteries, can't afford them, Yuasa are my preference.