Question: Just before Doc shows his plan with the DeLorean and the train Marty checks the walkie-talkies and Doc confirms it that they work. How are they able to get the walkie-talkies to work in 1885? I'm thinking Doc invented something so Doc and Marty can communicate with each other with them.
Kevin l Habershaw
19th Feb 2021
Back to the Future Part III (1990)
Answer: Given Doc's scientific ability (and some suspension of disbelief) it would be easy enough to rig up a makeshift battery that would last long enough. Or indeed they've just got lucky and the walkie-talkies' batteries still have enough life in them. They're not mobile phones, they don't need masts or any infrastructure, they just connect directly to each other.
Like you said, walkie-talkies work independently of any infrastructure, which is what I think the question was more about. However, the battery was invented way before 1885 with the first lead acid rechargeable battery being invented in 1859 with pasted electrode batteries being invented in the 1880's. So it's less about Doc rigging up a battery and just using what's already available or charging the batteries it came with (if we are assuming the batteries ran out of power).
The best batteries they had in those days were crude, wet batteries made out of earthenware and filled with sulphuric acid. They were cumbersome, dangerous and didn't have a lot of voltage or low current. Hardly suitable for a walkie-talkie that needs at least 9 volts. But I suppose it's possible Doc had some charged self-made batteries sitting at home to keep them going.
Definitely not "crude", certainly not as advanced as today, but the lead acid battery is the same technology a lot of batteries use today. They even had electric vehicles prior to 1885. My point was Doc didn't have to invent technology that didn't exist (as opposed to what some say he would have to do to get an 80's camcorder to play on a 50's TV). They had rechargeable batteries back then so it wouldn't be a stretch that Doc could recharge the batteries he had.
Answer: 1955 Doc got him some new batteries ("Just in case, fresh batteries for your walkie talkie. Oh what about that floating device?") They only used them on the train so the batteries would still be charged. In regards to how they work, they don't rely on phone masts, satellites, WiFi etc as they send radio waves to each other and not to any sort of base station.
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Answer: Doc from 1955 told Marty "just in case, fresh batteries for your Walkie-Talkies."
Kevin l Habershaw ★