Coondog,
Back in my decade of DD days, I did have to jump start it a few times without any problems, but then they all could've been closer matched amps on both cars (as Olympic1.7 says above).
IMHO - the best option today is to carry one of those little lithium-ion battery pack with you & save both the space of carrying cables, & the hunt for a willing jumper, to help you the jumpee.
You can match the Li battery pack's amps to the car in question, but you do need to keep it charged. An added benefit is that you can recharge them from the lighter socket when the car is running, & they can also recharge your phone, laptop/tablet, run a small 12v LED TV, etc. off of them with their added connectors that usually come with them as a kit.
As for the trickle charger - those only do a slow charge & are "dumb" - so they too can boil a battery, just like a regular charger (or at least damage the battery. So never just leave it on the car, except over night or something short-ish.
I have a small solar trickle charger that I use on camping trips in the Westy & Anion T20 trailer (like an Airstream) to keep their house batteries charged, but they're getting some draw down while camping to offset the constant slow charge. Northern Tool sells a 2-pack of them at a good price when on sale, they're made in China IIRC for Coleman, & are about 6" x 15" & put out about 5A max. IIRC. Handy to have for campers, when you're away from the wall plugs. They are not "smart" maintainers, so they do need to be watched.
What you need is a "battery maintainer" - which has sensors to detect when, how much & how long the battery needs topped-off, then it goes to sleep until next needed - while hooked up continuously.
They also make units to charge multiple cars - so you can also keep that gorgeous SS charged up off the same unit - if both can be parked together!
There are several good ones out there, & everyone has their fav for both the jump-packs & maintainers, so I won't go into names - but you can do some quick online research on them to pick your preference.
Also, you may be able to go online to the KOCE or KLCS local PBS station affiliate up there in A-valley or the overall PBS website, & go to the "MotorWeek" proigram, & look for the Pat Goss segment on trickle vs. maintainer segment from maybe 2014 or 15 for a quick overview on both the battery charger packs & the maintainers (latter was the oldest show).
I'm in the process of equipping all of our vehicles with those battery emergency pack chargers, starting with one for our `88 Westy. In my case I'm getting one from aftermarket suppliers for each car make, since they've used &/or tested them on the particular car. So after trying this first one out for a while, I'll get the one from BavAuto for my `85 325e BMW E30 - unless they say the one below is okay.
So I got the Westy one from GoWesty.com for the Vnagon based `88 Westy, but it may be good on the 914, since they also cover older "Splitty" & "Bay Window" VW vans - the latter of which ran our 2.0 motors (as did the 1st 80-83 Vanagons).
Otherwise, Porsche sells their own branded maintainer if you want the cache of Porsche (try Sunset or Suncoast Porsche for best parts pricing from P-dealers). I'll probably get that one when we finally find that "perfect" lightly used `08-12/13 Cayenne S that we're looking for as a tow vehicle for the Avion.
Good Luck!
Tom
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