So these "lite" wallets connect to a remote node and, query the transaction data from them through a rpc interface and scan through it on their side. They trust the remote node to speak the truth when scanning to not feed it fake transaction data. So in the worst case you might calculate a faked balance and transaction history.
Well in the worst case you use 100% until your battery dies and find nothing?
Most bip158 light wallets don't do much checking either, their worst case is limited to downloading all blocks. Which in practice also means a dead battery an no transaction history.
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